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Objectives Single umbilical artery (SUA) is associated with congenital malformations in most organ systems, but reported findings have not been consistent. While it has been suggested that genetic and persisting environmental factors influence the development of SUA, it is not known whether there is an increased risk of recurrence in a subsequent pregnancy of the same woman. The aims of this study were to investigate the occurrence of, and risk factors for, SUA in Norway, to assess its association with congenital malformations and trisomies 13, 18 and 21 and to study the risk of recurrence of SUA in subsequent pregnancies. Methods This was a population-based study of all (n = 918 933) singleton pregnancies of > 16 weeks' gestation recorded in the Medical Birth Registry of Norway from 1999 to 2014. To identify risk factors and congenital malformations associated with SUA, generalized estimating equations and logistic regression were used to calculate odds ratios (OR) with 95% CIs. ORs were also calculated for the recurrence of SUA in subsequent pregnancy. Results The occurrence of SUA in our population was 0.46% (4241/918 933). Parity ≥ 4, smoking, maternal pregestational diabetes, epilepsy, chronic hypertension, previous Cesarean delivery and conception by assisted reproductive technology increased the odds of having SUA. There was a particularly strong association between SUA and gastrointestinal atresia or stenosis in the neonate, with ORs of 25.8 (95% CI, 17.0-39.1) and 20.3 (95% CI, 13.4-30.9) for esophageal and anorectal atresia or stenosis, respectively, followed by an OR of 5.9 (95% CI, 1.9-18.5) for renal agenesis. SUA was associated with an up to 7-8 times increased risk of congenital heart defects. There was an association with microcephaly, congenital hydrocephalus and other congenital malformations of the brain and spinal cord. Diaphragmatic hernia, limb reductions and cleft lip or palate had a weaker association with SUA, with ORs ranging from 4.8 to 2.8. The associations with trisomy 18 and 13 were equally strong (OR 14.4 (95% CI, 9.3-22.4) and OR 13.6 (95% CI, 6.7-27.8), respectively), and the risk of trisomy 21 was doubled (OR 2.1 (95% CI, 1.2-3.6)). Pregnancies with SUA, with or without an associated malformation, had a 2-fold increased risk for SUA in a subsequent pregnancy. Conclusions SUA is associated strongly with gastrointestinal atresia or stenosis, suggesting common developmental mechanisms. The increased risk of recurrence of SUA suggests that genetic and/or persisting environmental factors influence the risk. We found that SUA had equally strong associations with trisomies 13 and 18. © 2019 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Purpose This study examines individual aggregation of postpartum hemorrhage (PPH), paternal contribution and how offspring birthweight and sex influence recurrence of PPH. Further, we wanted to estimate the proportion of PPH cases attributable to a history of PPH or current birthweight. Methods We studied all singleton births in Norway from 1967 to 2017 using data from Norwegian medical and administrational registries. Subsequent births in the parents were linked. Multilevel logistic regression was used to calculate odds ratios (ORs) with 95% confidence intervals (CI) for PPH defined as blood loss > 500 ml, blood loss > 1500 ml, or the need for blood transfusion in parous women. Main exposures were previous PPH, high birthweight, and fetal sex. We calculated adjusted population attributable fractions for previous PPH and current high birthweight. Results Mothers with a history of PPH had three- and sixfold higher risks of PPH in their second and third deliveries, respectively (adjusted OR 2.9; 95% CI 2.9–3.0 and 6.0; 5.5–6.6). Severe PPH (> 1500 ml) had the highest risk of recurrence. The paternal contribution to recurrence of PPH in deliveries with two different mothers was weak, but significant. If the neonate was male, the risk of PPH was reduced. A history of PPH or birthweight ≥ 4000 g each accounted for 15% of the total number of PPH cases. Conclusion A history of PPH and current birthweight exerted strong effects at both the individual and population levels. Recurrence risk was highest for severe PPH. Occurrence and recurrence were lower in male fetuses, and the paternal influence was weak.

Introduction Isolated single umbilical artery (iSUA) refers to single umbilical artery cords with no other fetal malformations. The association of iSUA to adverse outcome of pregnancy has not been consistently reported, and whether iSUA carries increased risk of third stage of labor complications has not been studied. We aimed to investigate the risk of adverse perinatal outcome, third stage of labor complications, and associated placental and cord characteristics in pregnancies with iSUA. A further aim was to assess the risk of recurrence of iSUA and anomalous cord or placenta characteristics in Norway. Material and methods This was a population-based study of all singleton pregnancies with gestational age >16 weeks at birth using data from the Medical Birth Registry of Norway from 1999 to 2014 (n = 918 933). Odds ratios (OR) with 95% confidence intervals were calculated for adverse perinatal outcome (preterm birth, perinatal and intrauterine death, low Apgar score, transferral to neonatal intensive care ward, placental and cord characteristics [placental weight, cord length and knots, anomalous cord insertion, placental abruption and previa]), and third stage of labor complications (postpartum hemorrhage and the need for manual placental removal or curettage) in pregnancies with iSUA, and recurrence of iSUA using generalized estimating equations and logistic regression. Results Pregnancies with iSUA carried increased risk of adverse perinatal outcome (OR 5.06, 95% confidence interval [CI] 4.26-6.02) and perinatal and intrauterine death (OR 5.62, 95% CI 4.69-6.73), and a 73% and 55% increased risk of preterm birth and small-for-gestational-age neonate, respectively. The presence of iSUA also carried increased risk of a small placenta, placenta previa and abruption, anomalous cord insertion, long cord, cord knot and third stage of labor complications. Women with iSUA, long cord or anomalous cord insertion in one pregnancy carried increased risk of iSUA in the subsequent pregnancy. Conclusions The presence of ISUA was associated with a more than five times increased risk of intrauterine and perinatal death and with placental and cord complications. The high associated risk of adverse outcome justifies follow up with assessment of fetal wellbeing in the third trimester, intrapartum surveillance and preparedness for third stage of labor complications.

INTRODUCTION Trial of labor (TOLAC) is an option in most preganancies after a cesarean section The objective of the study was to compare perinatal outcome in TOLAC and non-TOLAC deliveries in a population with high TOLAC rates. MATERIAL AND METHODS This was a cohort study based on population data from the Medical Birth Registry of Norway. We included term, cephalic, single, second deliveries, 1989-2009, after a first cesarean section (n = 43 422). TOLAC, TOLAC failure, non-TOLAC deliveries, and after high-risk and low-risk pregnancies (no risk/any risk), were compared with respect to offspring mortality, 5-minute Apgar score Apgar

INTRODUCTION The human yolk sac provides the embryo with stem cells, nutrients, and gas exchange. We hypothesized that more maternal resources, reflected in body size and body composition, would condition a a larger yolk sac, ensuring resources for the growing embryo. Thus, we aimed to determine the relation between maternal size in early pregnancy and yolk sac size. MATERIAL AND METHODS This subsidiary study was embedded in the multinational World Health Organization fetal growth project that included healthy women with a body mass index of 18-30, reliable information of their regular last menstrual period and singleton pregnancies. Yolk sac diameter, crown-rump length, and maternal height, weight, body mass index, and body composition were assessed before 13 weeks of gestation, and the fetal biometry was repeated during the pregnancy. RESULTS Of 140 participants, 122 with a successful yolk sac measurement were entered in the present analysis. Maternal weight was negatively associated with the yolk sac diameter (P = 0.007) and so was maternal height (P = 0.011), fat mass (P = 0.037), and lean body mass (P = 0.018), but not body mass index (P = 0.121). Significant effects were predominantly due to the female embryos and could be traced at 24 weeks of gestation. That is, a small yolk sac : crown-rump length ratio in early pregnancy was associated with a high fetal abdominal circumference (P

Introduction Cesarean section is the single most important risk factor for postpartum infection. Where the rest of the world shows increasing trends, the cesarean section rates are low in Norway and risk factors for infection after cesarean section may differ in high and low cesarean section settings. The goal of this study was to examine independent risk factors for surgical site infection after cesarean delivery in a setting of low cesarean section rates. Material and methods We conducted a hospital-based case-control study at Haukeland University Hospital. We included women who presented to our hospital with surgical site infection after cesarean section during the years 2014–2016 (n = 75). Controls were selected at a ratio of 2:1 (n = 148). Cases and controls were compared with respect to maternal and pregnancy characteristics using uni- and multivariable logistic regression models. Main outcome measures were anticipated risk factors for surgical site infection. Results The occurrence of surgical site infection was 0.4% and 5.4% after elective and emergency cesarean section, respectively. Compared to women without surgical site infection, women with surgical site infection were almost thrice more obese before pregnancy (OR 2.8, 95% CI 1.2–7.0), four times more likely to have preexisting psychiatric conditions (OR 4.4, 95% CI 1.1–17.6), and five times more likely to receive blood transfusion (OR 5.1, 95% CI 1.4–18.8). Signs of infection during labor was a marginally significant risk factor for surgical site infection (OR 2.0, 95% CI 1.0–5.4). Conclusions Emergency cesarean section was a significant risk factor for surgical site infection. Pregestational obesity, preexisting psychiatric conditions, and blood transfusion during or following delivery, were independent risk factors for surgical site infection. Signs of infection during labor was a marginally significant risk factor. Women with either of these risk factors should be carefully monitored and evaluated for signs of infection in the postpartum period. publishedVersion

Introduction Studies on the family aggregation of postpartum hemorrhage (PPH) are scarce and with inconsistent results, and to what extent current birthweight influences recurrence between relatives remains to be studied. Further, family aggregation of PPH has been studied from an individual, but not from a public heath perspective. We aimed to investigate family aggregation of PPH in Norway, how birthweight influences these effects, and to estimate the proportion of PPH cases attributable to a family history of PPH and current birthweight. Material and methods Using data from the Medical Birth Registry of Norway, Statistics Norway, and Central Population Registry of Norway we identified individuals as newborns, parents, grandparents, and full and half-siblings, and studied 1 002 687 mother–offspring, 841 164 father–offspring, and 761 011 both-parents–offspring pairs. We used multilevel logistic regression to calculate odds ratios (OR) with 95% CI. Results If the birth of the mother but not of the father involved PPH, then the OR of PPH (>500 mL) in the next generation was 1.44 (95% CI 1.39–1.49). If the birth of the father but not of the mother involved PPH, then OR was 1.12 (95% CI 1.08–1.16). These effects were stronger in severe PPH. Recurrence between siblings was highest between full sisters (OR 1.47, 95% CI 1.41–1.52), followed by maternal half-sisters, paternal half-sisters, and partners of full brothers. A family history of PPH or birthweight of 4000 g or more accounted for ≤5% and 15% of the total number of PPH cases, respectively. Conclusions A history of PPH in relatives influenced the recurrence risk of PPH in a dose–response pattern consistent with the anticipated proportion of shared genes. The recurrence was highest through the maternal line. publishedVersion

This is the peer reviewed version of the following article: Acharya, G., Ebbing, C., Karlsen, H., Kiserud, T. & Rasmussen, S. (2019). Sex-specific reference ranges of cerebroplacental and umbilicocerebral ratios: A longitudinal study. Ultrasound in Obstetrics and Gynecology, 2019, which has been published in final form at https://doi.org/10.1002/uog.21870. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Objectives - The ratio of middle cerebral artery (MCA) pulsatility index (PI) to umbilical artery (UA) PI, i.e. cerebro‐placental ratio (CPR), has been suggested as a measure of fetal “brain sparing” phenomenon reflecting redistribution of fetal cardiac output as a response to placental insufficiency. Observational studies have shown that low CPR values predict increased risk of adverse perinatal outcomes although evidence from randomized clinical trials is lacking. The inverse ratio, i.e. umbilico‐cerebral ratio (UCR), is preferred by some as it increases with increasing degree of fetal compromise. Monitoring fetal wellbeing requires serial assessment, and for this purpose, appropriate reference values should be based on data from longitudinal studies. However, longitudinal reference ranges for the UCR have not been established. Furthermore, the sex of the fetus influences its growth velocity, cord properties, in utero circadian rhythm, behavioral states and placental function, but whether gestational age‐dependent changes in CPR or UCR differ between male and female fetuses has not been studied. Thus, our objective was to investigate sex‐specific, gestational age‐associated serial changes in CPR and UCR during the second half of pregnancy and establish longitudinal reference ranges. Methods - This was a dual‐center prospective longitudinal study of singleton low risk pregnancies. Doppler blood flow velocity waveforms were obtained serially from the UA and MCA during 19‐41 weeks of gestation, and PIs were determined. CPR and UCR were calculated as the ratios, MCA PI/ UA PI and UA PI/ MCA PI, respectively. The course and outcome of pregnancies was recorded. Sex of the fetus was determined after delivery. Reference intervals were constructed using multilevel modelling and gestational age‐specific Z‐scores of male and female fetuses were compared. Results - Of a total of 299 pregnancies enrolled, 284 women and their fetuses (148 male and 136 female) were included in the final analysis, and 979 paired measurements of UA and MCA PIs were used to construct sex‐specific longitudinal reference intervals. Both CPR and UCR had U‐shaped curves of development during pregnancy, but with opposite directions. There was a small but significant (P=0.007) difference in z‐scores of CPR and UCR between male and female fetuses throughout the second half of pregnancy. Conclusions - We have established longitudinal reference ranges for CPR and UCR suitable for serial monitoring with possibilities to refine the assessment by fetal sex‐specific ranges and the conditioning by a previous measurement. The clinical significance of such refinements needs further evaluation.

Introduction: In pregnancies after a previous cesarean section (CS), a planned repeat CS delivery has been associated with excess risk of adverse outcome. However, also the alternative, a trial of labor after CS (TOLAC), has been associated with excess risks. A TOLAC failure, involving a non-planned CS, carries the highest risk of adverse outcome and a vaginal delivery the lowest. Thus, the decision regarding delivery mode is pivotal in clinical handling of these pregnancies. However, even with a high TOLAC rate, as seen in Norway, repeat CSs are regularly performed for no apparent medical reason. The objective of the present study was to assess to which extent demographic, socioeconomic, and health system factors are determinants of TOLAC and TOLAC failure in low risk pregnancies, and whether any effects observed changed with time. Materials and methods: The study group comprised 24 645 second deliveries (1989–2014) after a first delivery CS. Thus, none of the women had prior vaginal deliveries or more than one CS. Included pregnancies were low risk, cephalic, single, and had gestational age ≥ 37 weeks. Data were obtained from the Medical Birth Registry of Norway (MBRN). The exposure variables were (second delivery) maternal age, length of maternal education, maternal country of origin, size of the delivery unit, health region (South-East, West, Mid, North), and maternal county of residence. The outcomes were TOLAC and TOLAC failure, as rates (%), relative risk (RR) and relative risk adjusted (ARR). Changes in determinant effects over time were assessed by comparing rates in two periods, 1989–2002 vs 2003–2014, and including these periods in an interaction model. Results: The TOLAC rate was 74.9%, with a TOLAC failure rate of 16.2%, resulting in a vaginal birth rate of 62.8%. Low TOLAC rates were observed at high maternal age and in women from East Asia or Latin America. High TOLAC failure rates were observed at high maternal age, in women with less than 11 years of education, and in women of non-western origin. The effects of health system factors, i.e. delivery unit size and administrative region were considerable, on both TOLAC and TOLAC failure. The effects of several determinants changed significantly (P < 0.05) from 1989–2002 to 2003–2014: The association between non-TOLAC and maternal age > 39 years became weaker, the association between short education and TOLAC failure became stronger, and the association between TOLAC failure and small size of delivery unit became stronger. Conclusion: Low maternal age, high education, and western country of origin were associated with high TOLAC rates, and low TOLAC failure rates. Maternity unit characteristics (size and region) contributed with effects on the same level as individual determinants studied. Temporal changes were observed in determinant effects. publishedVersion

Background Socioeconomic (SE) inequalities have been observed in a number of adverse outcomes of pregnancy and many of the risk factors for such outcomes are associated with a low SE level. However, SE inequalities persist even after adjustment for these risk factors. Less well-off women are more vulnerable, but may also get less adequate health services. The objective of the present study was to assess possible associations between SE conditions in terms of maternal education as well as ethnic background and obstetric care. Methods A population-based national cohort study from the Medical Birth Registry of Norway. The study population comprised 2 305 780 births from the observation period 1967–2009. Multilevel analysis was used because of the hierarchical structure of the data. Outcome variables included induction of labour, epidural analgesia, caesarean section, neonatal intensive care and perinatal death. Results While medical interventions in the 1970s were employed less frequently in women of short education and non-western immigrants, this difference was eliminated or even reversed towards the end of the observation period. However, an excess perinatal mortality in both the short-educated [adjusted relative risk (aRR) = 2.49] and the non-western immigrant groups (aRR = 1.75) remained and may indicate increasing health problems in these groups. Conclusion Even though our study suggests a fair and favourable development during the last decades in the distribution across SE groups of obstetric health services, the results suggest that the needs for obstetric care have increased in vulnerable groups, requiring a closer follow-up.

INTRODUCTION Despite adequate glycemic control, the risks of fetal macrosomia and perinatal complications are increased in diabetic pregnancies. Adjustments of the umbilical venous distribution, including increased ductus venosus shunting, can be important fetal compensatory mechanisms, but the impact of pregestational diabetes on umbilical venous and ductus venosus flow is not known. MATERIAL AND METHODS In this prospective study, 49 women with pregestational diabetes mellitus underwent monthly ultrasound examinations from gestational week 20 to 36. The blood velocity and the mean diameters of the umbilical vein and ductus venosus were used for calculating blood flow volumes. The development of the umbilical venous flow, ductus venosus flow and ductus venosus shunt fraction (% of umbilical venous blood shunted through the ductus venosus) was compared with a reference population, and the effect of HbA1c on the ductus venosus flow was assessed. RESULTS The umbilical venous flow was larger in pregnancies with pregestational diabetes mellitus than in low-risk pregnancies (p

This is the peer reviewed version of the following article: Rossen, J., Klungsøyr, K., Albrechtsen, S., Løkkegård, E., Rasmussen, S., Bergholt, T. & Skjeldestad, F.E. (2018). Can oxytocin augmentation modify the risk of epidural analgesia by maternal age in cesarean sections? Acta Obstetricia et Gynecologica Scandinavica, 97(7), 872-879, which has been published in final form at https://doi.org/10.1111/aogs.13341. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Introduction: Maternal age is an established risk factor for cesarean section; epidural analgesia and oxytocin augmentation may modify this association. We investigated the effects and interactions of oxytocin augmentation, epidural analgesia and maternal age on the risk of cesarean section. Material and methods: In all, 416 386 nulliparous women with spontaneous onset of labor, ≥37 weeks of gestation and singleton infants with a cephalic presentation during 2000–2011 from Norway and Denmark were included [Ten‐group classification system (Robson) group 1]. In this case‐control study the main exposure was maternal age; epidural analgesia, oxytocin augmentation, birthweight and time period were explanatory variables. Chi‐square test and logistic regression were used to estimate associations and interactions. Results: The cesarean section rate increased consistently with advancing maternal age, both overall and in strata of epidural analgesia and oxytocin augmentation. We observed strong interactions between maternal age, oxytocin augmentation and epidural analgesia for the risk of cesarean section. Women with epidural analgesia generally had a reduced adjusted odds ratio when oxytocin was used compared with when it was not used. In Norway, this applied to all maternal age groups but in Denmark only for women ≥30 years. Among women without epidural, oxytocin augmentation was associated with an increased odds ratio for cesarean section in Denmark, whereas no difference was observed in Norway. Conclusions: Oxytocin augmentation in nulliparous women with epidural analgesia is associated with a reduced risk of cesarean section in labor with spontaneous onset.

Objective To assess whether parents who were born small for gestational age (below the 10th birthweight centile, SGA) have increased risk of severe or mild placental abruption. To assess whether a history of SGA in other family members modifies this intergenerational effect. Design Prospective population-based observational study. Setting The Medical Birth Registry of Norway. Population From 1967 to 2013, 785 333 mother–offspring pairs, 643 066 father–offspring pairs, 272 941 maternal tetrads (i.e. her offspring, sibling, and niece/nephew), and 265 505 paternal tetrads were identified. Methods Cohort study based on linked data from the Medical Birth Registry of Norway. Main outcome measures Relative risk (RR) of severe placental abruption (preterm birth, birthweight below the 10th centile, or perinatal death) and mild placental abruption (other cases) in families with SGA. Results Mothers who were born SGA had increased risk of severe placental abruption (RR 1.5; 95% confidence interval, 95% CI 1.3–1.8), but not mild abruption. The paternal effects were weaker. The combined effect of SGA in the mother and her sibling on severe abruption was twofold (RR 2.4; 95% CI 1.7–3.3) compared with birthweight centiles ≥10 for both. Similarly, the effect of adding an SGA niece/nephew was twofold (RR 2.3; 95% CI 1.3–3.9), whereas the combined effect of SGA in the mother, her sibling and her niece/nephew was fourfold (RR 3.6; 95% CI 1.9–6.8). Conclusions Women who were born SGA have an increased risk of severe placental abruption. The corresponding paternal effect was modest. A history of SGA in other family members increases the generational effect. Tweetable abstract Women born small for gestational age have excess risk of placental abruption.

Hypertensive disorders of pregnancy (HDP) tend to recur from one pregnancy to the next. The aims of the study were to assess the recurrence risk according to type of HDP defined by gestational age at birth and to examine whether recurrence is associated with the following additional risk factors for HDP: maternal age, smoking, inter delivery interval, diabetes, body mass index, as well as fetal growth restriction, and to assess temporal trends in these associations. All women with two singleton births in the Medical Birth Registry of Norway 1967-2012 (n= 742 980) were included in this population based cohort study. Logistic regression was used to calculate odds ratios for the risk of recurrent HDP according to type of HDP. The highest odds ratio of recurrence was observed for the same type of HDP based on gestational age at delivery. After gestational hypertension and term preeclampsia the risk increased tenfold for the same type to recur, whereas after late and early preterm preeclampsia, the risk increased 27 and 97 fold, respectively. The recurrence of early preterm preeclampsia was less influenced by additional risk factors than term HDP. Recurrence of early preterm HDP was significantly lower from 1993 onwards. Recurrent HDP tended to be of the same type as the previous HDP. Risk of recurrence associated with additional risk factors were observed particularly after term. The odds ratio of recurrence of early preterm HDP was significantly lower from 1993 onwards. This article is protected by copyright. All rights reserved.

Anomalous cord insertion is associated with increased risk of adverse maternal and perinatal outcome. Our aim was to study whether anomalous cord insertion is associated with prelabor rupture of membranes (PROM), preterm PROM (pPROM), long or short umbilical cord, and time trend of spontaneous preterm birth (SPTB) and anomalous cord insertion.A population-based register study using data from the Medical Birth Register of Norway including all singleton births (gestational age16 weeks and45 weeks) during 1999-2013 (n = 860 465) to calculate odds ratios (ORs) for PROM, pPROM, SPTB, and cord length (95th or5th centile) according to the cord insertion site by logistic regression with adjustment for possible confounders. We also assessed time trends of SPTB and anomalous cord insertion.Velamentous insertion of the cord was associated with an increased risk of PROM (OR 1.6, 95% CI 1.5-1.7), pPROM (OR 2.7, 95% CI 2.4-3.0), SPTB (OR 2.0, 95% CI 1.9-2.2), and a short cord (OR 1.7, 95% CI 1.5-1.8). Marginal insertion was to a lesser extent associated with these complications. Occurrences of SPTB and anomalous insertion declined. The decline in SPTB persisted after including an interaction term between anomalous insertion and time.Velamentous and, to a lesser extent, marginal cord insertions were associated with increased risk of PROM, pPROM, SPTB, and short cord. This suggests a common pathogenesis behind altered function of the membranes, cord, and placenta. The decline in SPTB could not be explained by the reduction in the occurrence of anomalous cord insertion.

INTRODUCTION In most pregnancies after a cesarean section, a trial of labor is an option. The objective of the study was to explore trial of labor and its failure in pregnancies with medical risk conditions, in a population with a high trial of labor rate. MATERIAL AND METHODS In a cohort study (n = 57 109), using data from the Medical Birth Registry of Norway 1989-2014, women with a second delivery after a first pregnancy cesarean section were included. Preterm, multiple, and non-cephalic deliveries were excluded. The outcomes were trial of labor and failed trial of labor, assessed as rates and relative risk, using deliveries without risk conditions as reference. Temporal trends were assessed by 3-year periods. The exposures were selected medical risk conditions, ie previous offspring death, labor dystocia, diabetes, heart conditions, chronic hypertension, chronic kidney disease, rheumatoid arthritis, thyroid disease, asthma, prepregnancy psychiatric conditions, epilepsy, obesity, gestational diabetes, eclampsia and preeclampsia, gestational hypertension, major malformations, second-pregnancy psychiatric conditions, assisted reproduction, macrosomia, and small-for-gestational-age neonates. Induced onset of labor was compared with spontaneous onset of labor for each condition studied. RESULTS In risk pregnancies (n = 31 994) the trial of labor rate was 64.9% and failure rate was 27.6%, compared with 74.6% and 16.4% in pregnancies without any of the risk conditions studied (n = 25 115). The lowest trial of labor rates were observed in diabetes type 1 (49.5%), diabetes type 2 (46.7%), maternal heart conditions (54.5%), and pregnancy-related psychiatric conditions (19.7%). The highest failure rates were observed in diabetes type 1 (43.1%), diabetes type 2 (40.3%), maternal obesity (36.9%), gestational diabetes (36.0%), and offspring macrosomia (43.0%). Induced labor was associated with failed trial of labor (P

Background Pregestational diabetes is associated with fetal macrosomia, and umbilical perfusion of the fetal liver has a role in regulating fetal growth. We therefore hypothesized that pregestational diabetes alters fetal liver blood flow depending on degree of glycemic control. Methods In a prospective study, 49 women with pregestational diabetes underwent monthly ultrasound examinations during 24-36 gestational weeks. Blood flow was determined in the umbilical vein, ductus venosus and portal vein, and blood velocity was measured in the left portal vein, the latter reflecting the watershed between splanchnic and umbilical flow. The measurements were compared with reference values by z-score statistics, and the effect of HbA 1c assessed. Results The umbilical venous flow to the liver (z-score 0.36, p = 0.002), total venous liver flow (z-score 0.51, p1C . Conclusions In spite of increased umbilical blood distribution to the fetal liver, graded according to glycemic control, the total venous liver flow did not match third trimester fetal growth in pregnancies with pregestational diabetes, thus contributing towards increased perinatal risks and possibly altered liver function with long-term metabolic consequences.

OBJECTIVE To test whether adding conditional growth centiles to size centiles of estimated fetal weight (EFW) improves prediction of adverse perinatal outcome in pregnancies with or at risk of having a small-for-gestational-age (SGA) fetus. METHODS This prospective longitudinal study included pregnant women at risk of or diagnosed with an SGA (≤ 5(th) centile) fetus. They underwent serial ultrasound measurements and the final two were included in the analyses for this study. The EFW was categorized into normal (> 5(th) or 10(th) centile) and abnormal (≤ 5(th) or 10(th) centile) for size and conditional growth before entering the variables into log-binomial regression analyses. Adverse outcomes were delivery

The human yolk sac provides the embryo with stem cells, nutrients, and gas exchange. We hypothesized that more maternal resources, reflected in body size and body composition, would condition a a larger yolk sac, ensuring resources for the growing embryo. Thus, we aimed to determine the relation between maternal size in early pregnancy and yolk sac size.This subsidiary study was embedded in the multinational World Health Organization fetal growth project that included healthy women with a body mass index of 18-30, reliable information of their regular last menstrual period and singleton pregnancies. Yolk sac diameter, crown-rump length, and maternal height, weight, body mass index, and body composition were assessed before 13 weeks of gestation, and the fetal biometry was repeated during the pregnancy.Of 140 participants, 122 with a successful yolk sac measurement were entered in the present analysis. Maternal weight was negatively associated with the yolk sac diameter (P = 0.007) and so was maternal height (P = 0.011), fat mass (P = 0.037), and lean body mass (P = 0.018), but not body mass index (P = 0.121). Significant effects were predominantly due to the female embryos and could be traced at 24 weeks of gestation. That is, a small yolk sac : crown-rump length ratio in early pregnancy was associated with a high fetal abdominal circumference (P 0.001) and estimated fetal weight (P = 0.001).The human yolk sac is involved in the regulation of embryonic growth, but contrary to our hypothesis, the yolk sac has a compensatory capacity, being larger when the mothers are smaller; and the effect can be traced on fetal size at 24 weeks of gestation.

INTRODUCTION Fetal biometry is used for determining gestational age and estimated date of delivery (EDD). However, the accuracy of the EDD depends on the assumed length of pregnancy included in the calculation. This study aimed at assessing the actual pregnancy length and accuracy of EDD prediction based on fetal head circumference measured at the second trimester. MATERIAL AND METHODS This was a population-based observational study with the following inclusion criteria: singleton pregnancy, head circumference dating in the second trimester, spontaneous onset or induction of delivery ≥ 294 days of gestation, live birth. The EDD was set anticipating a pregnancy length of 282 days. Bias in the prediction of EDD was defined as the difference between the actual date of birth and the EDD. RESULTS Head circumference measurements were available for 21 451 pregnancies. Ultrasound-dated pregnancies had a median pregnancy length of 283.03 days, corresponding to a method bias of 1.03 days (95% CI; 0.89-1.16). This bias was dependent on the head circumference at dating, ranging from -1.58 days (95% CI; -3.54 to 1.12) to 3.42 days (95% CI; 1.98-4.31). The median pregnancy length, based on the last menstrual period of women with a regular menstrual cycle (n = 12 985), was 283.15 days (95% CI; 282.91-283.31). A total of 5685 (22.9%, 95% CI; 22.4% to 23.4%) and 886 women (3.6%, 95% CI; 3.3%-3.8%) were still pregnant 7 and 14 days after the EDD, respectively. CONCLUSIONS Second trimester head circumference measurements can be safely used to predict EDD. A revision of the pregnancy length to 283 days will reduce the bias of EDD prediction to a level comparable with other methods.

Background To investigate whether the occurrence of preeclampsia varied by maternal reasons for immigration. Methods We included 1,287,270 singleton pregnancies (163,508 to immigrant women) in Norway during 1990–2013. Individual data were obtained through record linkage between the Medical Birth Registry of Norway and Statistics Norway. Analyses were performed for preeclampsia overall and in combination with preterm birth

Objectives To determine risk factors for short and long umbilical cord, entanglement and knot. Explore their associated risks of adverse maternal and perinatal outcome, including risk of recurrence in a subsequent pregnancy. To provide population based gestational age and sex and parity specific reference ranges for cord length. Design Population based registry study. Setting Medical Birth Registry of Norway 1999–2013. Population All singleton births (gestational age>22weeks

To assess whether anomalous cord insertion is associated with risk of complications in the third stage of labor.A population-based study.Norwegian Medical Birth Register.All singleton births (gestational age16 weeks and45 weeks) during the period 1999-2011 (n = 738,443 singletons). Deliveries by cesarean were excluded, leaving 628,680 vaginal singleton deliveries for the analyses.Calculation of odds ratios for complications in the third stage of labor (postpartum hemorrhage, manual delivery of the placenta, curettage) in velamentous and marginal cord insertion by logistic regression with adjustment for confounders.Complications in the third stage of labor, postpartum hemorrhage, manual placental removal and curettage.Anomalous cord insertion was associated with an increased risk of complications in the third stage of labor, the risk being higher for velamentous than for marginal insertion. The risks persisted after adjusting for possible confounding factors. Velamentous cord insertion carried a 5.6% risk of a need for manual removal of the placenta, compared with the risk of 1.1% for nonvelamentous insertion (odds ratio = 5.21, 95% confidence interval 4.71-5.76) in vaginal delivery, and we found increased risks of curettage (odds ratio = 3.29, 95% confidence interval 2.87-3.77) and postpartum hemorrhage (odds ratio = 2.06, 95% confidence interval 1.77-2.39).Marginal and especially velamentous cord insertion is associated with an increased risk of hemorrhage in the third stage of labor, need for manual removal of the placenta and curettage. Anomalous cord insertion can be identified prenatally and so possibly influence obstetric management.

Objective To assess whether the reported excess of large for gestational age (LGA) neonates in pre-eclamptic women delivering at term is attributable to maternal obesity. Design, setting and population Population-based observational study including 77 294 singleton pregnancies registered in the Medical Birth Registry of Norway between 2007 and 2010. Methods Comparison of birthweight percentiles and z-scores between women with and without pre-eclampsia. Main outcome measures Odds ratio (OR) of LGA and z-scores of birthweight in relation to pre-eclampsia. Results Pre-eclamptic women delivering at term had increased risk of having LGA neonates. Unadjusted ORs with 95% confidence interval (95% CI) of LGA above the 90th and 95th birthweight centiles were 1.4, 95% CI 1.2–1.6 and 1.6, 95% CI 1.3–1.9, respectively. The excess of LGA persisted after including gestational diabetes and diabetes types 1 and 2 in a multivariate analysis (corresponding ORs 1.3, 95% CI 1.1–1.5 and 1.4, 95% CI 1.2–1.7), but disappeared after adjusting for maternal prepregnant body mass index (ORs 1.1, 95% CI 0.9–1.2 and 1.1, 95% CI 0.9–1.3). Conclusions This study suggests accelerated fetal growth in a subset of pre-eclamptic women delivering at term. The excess of LGA neonates is attributable to maternal obesity among pre-eclamptic women delivering at term. The maternal obesity epidemic may lead to an increased prevalence of both pre-eclampsia and LGA neonates among women delivering at term.

Objective To investigate the association between advanced maternal age and adverse pregnancy outcomes and to compare the risks related to advanced maternal age with those related to smoking and being overweight or obese. Methods A population-based register study including all nulliparous women aged 25 years and older with singleton pregnancies at 22 weeks of gestation or greater who gave birth in Sweden and Norway from 1990 to 2010; 955,804 women were analyzed. In each national sample, adjusted odds ratios (ORs) of very preterm birth, moderately preterm birth, small for gestational age, low Apgar score, fetal death, and neonatal death in women aged 30-34 years (n=319,057), 35-39 years (n=94,789), and 40 years or older (n=15,413) were compared with those of women aged 25-29 years (n=526,545). In the Swedish sample, the number of additional cases of each outcome associated with maternal age 30 years or older, smoking, and overweight or obesity, respectively, was estimated in relation to a low-risk group of nonsmokers of normal weight and aged 25-29 years. Results The adjusted OR of all outcomes increased by maternal age in a similar way in Sweden and Norway; and the risk of fetal death was increased even in the 30- to 34-year-old age group (Sweden n=826, adjusted OR 1.24, 95% confidence interval [CI] 1.13-1.37; Norway n=472, adjusted OR 1.26, 95% CI 1.12-1.41). Maternal age 30 years or older was associated with the same number of additional cases of fetal deaths (n=251) as overweight or obesity (n=251). Conclusion For the individual woman, the absolute risk for each of the outcomes was small, but for society, it may be significant as a result of the large number of women who give birth after the age of 30 years. Level of evidence II.

Objective. To determine the association between 5-min Apgar score and umbilical cord artery carbon dioxide tension (pCO2). Design. Observational study. Setting. European hospital labor wards. Population. Data from 36 432 newborns � 36 gestational weeks were obtained from three sources: two trials of monitoring with fetal electrocardiogram (the Swedish randomized controlled trial and the European Union Fetal ECG trial) and M€ Hospital data. After validation of the acid–base values, 25 806 5-min Apgar scores were available for analysis. Methods. Validation of the umbilical cord acid–base values was performed to obtain reliable data. 5-min Apgar score was regressed against cord artery pCO2 in a polynomial multilevel model. Main outcome measures. Five-min Apgar score, umbilical cord pCO2, pH, and base deficit. Results. Overall, a higher cord artery pCO2 was found to be associated with lower 5-min Apgar scores. However, among newborns with moderate acidemia, lower umbilical cord artery pCO2 ( � median pCO2 for the specific cord artery pH) was associated with lower 5-min Apgar scores, with a relative risk of 2.0 (95% confidence interval: 1.4–2.8) for 5-min Apgar scores 0–6. Conclusions. Metabolic acidosis affects the newborn’s vitality more than respiratory acidosis. In addition, elevated levels of pCO2 may be beneficial for fetuses with moderate acidemia, and thus cord artery pCO2 is a factor that should be considered when assessing the compromised newborn. Abbreviations: AUC, area under the curve; BDecf, base deficit in the extracellular fluid; CI, confidence interval; CTG, cardiotocography; EU-STAN, European Union Fetal electrocardiogram multicenter trial; pCO2, carbon dioxide tension; ROC, receiver operating characteristic; SRCT, Swedish randomized controlled trial on intrapartum fetal monitoring; STAN, CTG with automatic ST-interval analysis of the fetal electrocardiogram.

Objective To investigate the aggregation of obstetric anal sphincter injuries (OASIS) in relatives. Design Population-based cohort study. Setting The Medical Birth Registry of Norway from 1967 to 2008. Population All singleton, vertex-presenting infants weighing 500 g or more. Through linkage by national identification numbers, 393 856 mother–daughter pairs, 264 675 mother–son pairs, 134 889 mothers whose sisters later became mothers, 132 742 fathers whose brothers later became fathers, 131 702 mothers whose brothers later became fathers and 88 557 fathers whose sisters later became mothers were provided. Methods Comparison of women with and without a history of OASIS in their relatives. Main outcome measure Relative risk of OASIS after a previous OASIS in the family. Results The risk of OASIS was increased if the woman's mother or sister had OASIS in a delivery (aRR 1.9, 95% CI 1.6–2.3; aRR 1.7, 95% CI 1.6–1.7, respectively). If OASIS occurred in one brother's partner at delivery, the risk of OASIS in the next brother's partner was modestly increased (aRR 1.2, 95% CI 1.1–1.4). If OASIS occurred in one sister at delivery, the risk of OASIS in the brother's partner was also increased a little (aRR 1.2, 95% CI 1.1–1.4). However, there was no excess occurrence in sisters whose brothers' partners had previously had OASIS (aRR 1.1, 95% CI 0.9–1.3). Conclusions There appears to be increased familial aggregation of OASIS. These risks are stronger through the maternal rather than the paternal line of transmission, suggesting a strong genetic role that shapes aggregation of OASIS within families. These observations must be cautiously interpreted because of bias from unmeasured confounding factors may have impacted the findings.

Introduction A validation of data regarding the placenta, cord and membranes in Medical Birth Registry of Norway (MBRN) is lacking. Here we investigate the inter- and intra-observer agreement of observations regarding the placenta, cord and membranes to the MBRN in two institutions. Material and methods We conducted a dual center validation study of data regarding placenta, cord and membranes. In the inter-observer study, 196 placentas in two institutions were examined by the attending midwife and a blinded colleague, whereas in the intra-observer study registrations by the attending midwife on 195 placentas were compared with her own registrations to the MBRN. In a separate sample consisting of 51 placental pathology reports, midwives’ registrations to the MBRN were compared with the pathology report. For categorical and continuous variables, agreement was assessed by kappa value and paired sample t-test, respectively. Results Inter-observer agreement between two midwives for cord insertion site and bi-placenta, cord knots and vessel anomalies were good (kappa values >0.79 and >0.96, respectively). The inter- and intra-observer study showed no significant differences regarding placental weight and cord length (p = 0.31 and 0.28, p = 0.71 and 0.39, respectively). The inter-observer agreement between the pathology reports and midwives’ registrations was good for gross placental and cord variants (kappa 0.73–1.0), but there were significant differences in placental weight and cord length (p < 0.0001). Conclusions The results suggest that the validity of data regarding placenta and cord in the MBRN is sufficiently high to justify future large-scale epidemiologic research based on this database.

Introduction Trial of labor (TOL) is an option in most deliveries after a previous cesarean section (CS). The Medical Birth Registry of Norway (MBRN) has received compulsory notification of all deliveries in the country since 1967, including data that could identify TOL in epidemiologic research. The objective of this study was to validate MBRN data for identification of TOL deliveries after a previous cesarean section (CS). Material and methods The MBRN provided a random national sample of 500 birth order two deliveries during 1989–2012 in women with a registered birth order one CS delivery. The reporting maternity units were asked to complete a questionnaire on data items in both deliveries, using hospital record data as the gold standard. Results Completed questionnaires were returned for 477 women (95.5%) with data on both deliveries. An algorithm to identify TOL using MBRN data from the birth order two delivery had a positive predictive value of 93.2%, a negative predictive value of 93.5%, a sensitivity of 96.1%, and a specificity of 88.8%. Validity of MBRN data on mode and onset of delivery, CS subtype, and planned mode of delivery is also reported. Conclusions MBRN data on planned and actual mode of delivery, CS subtype, and the algorithm to identify TOL in deliveries after a previous CS had satisfactory quality for a registry-based study of TOL.

Aims: Preterm birth is a major cause of perinatal mortality and morbidity and is strongly associated with socio-economic factors. The objective of this study was to examine the associations of maternal education, marital status and ethnicity with preterm birth and to determine the extent to which such associations can be explained by the established risk factors of maternal age, parity and smoking. Methods: This was a register-based cohort study with data from the Medical Birth Registry of Norway 1999–2009 and Statistics Norway. The sample included all singleton spontaneous births in Norway from 1999 to 2009 ( n=494,073). The main outcome measure was preterm birth (gestational age

Introduction. Centiles of middle cerebral artery pulsatility index and cerebroplacental ratio are useful for predicting adverse perinatal outcomes. A ‘conditional centile’ is conditioned by a previous measurement reflecting degree of individual change over time. Here we test whether such centiles are independent predictors and whether their combination improves prediction. Material and methods. This prospective longitudinal study included 220 pregnant women diagnosed with or at risk of having a small-for-gestational-age fetus. Serial Doppler measurements of the umbilical artery and middle cerebral artery pulsatility indexs were used to calculate cerebroplacental ratio. Preterm birth, operative delivery due to fetal distress, admission to neonatal intensive care unit, 5-min Apgar score

Please cite this paper as: Waldenstrom U, Gottvall K, Rasmussen S. Caesarean section in nulliparous women of advanced maternal age has been reduced in Sweden and Norway since the 1970s: a register-based study. BJOG 2012;119:1591–1596. Objective To investigate rates of caesarean delivery in Sweden and Norway from 1973 to 2008 in relation to advanced and very advanced maternal age. Design Register study. Setting Sweden and Norway. Sample All nulliparous women aged over 30 years with a singleton pregnancy, with the fetus in a cephalic presentation, and delivering at term between 1973 and 2008 were evaluated. The study population comprised 329 824 women in Sweden and 127 810 women in Norway. Methods Data from the national Medical Birth Registers were used to describe caesarean section rates in three age groups: 30–34 years (reference group); 35–39 years (advanced age group); and ≥40 years (very advanced age group). Logistic regression analyses estimated the risk in each age group over four decades, in each of the two national samples. Results Caesarean delivery decreased from 1973–1979 to 2000–2008 in the two oldest age groups in Sweden (35–39 years, OR = 0.53, 95% CI = 0.50–0.58; ≥40 years, OR = 0.36, 95% CI = 0.30–0.43) and Norway (35–39 years, OR = 0.61, 95% CI = 0.54–0.68; ≥40 years, OR = 0.45, 95% CI = 0.34–0.58), but increased in women aged 30–34 years. The caesarean delivery rate in the two oldest groups peaked in the second half of the 1970s. Regardless of time point, the caesarean delivery rate was always highest in women aged ≥40 years, followed by women aged 35–39 years and lowest in women aged 30–34 years. Conclusions Caesarean delivery in nulliparous women of advanced and very advanced age peaked by end of the 1970s in Sweden and Norway. The subsequent reduction was contemporaneous with the introduction of electronic fetal monitoring and a more consistent use of the partogram, suggesting that more effective surveillance of labour increased the chance of a vaginal birth in these high-risk women.

Please cite this paper as: Aasheim V, Waldenstrom U, Hjelmstedt A, Rasmussen S, Pettersson H, Schytt E. Associations between advanced maternal age and psychological distress in primiparous women, f ...

article i nfo Objectives: The superior vena cava (SVC) drains venous blood from the upper foetal body, mainly the head. Data on the human foetus is scarce. Here we present reference values for the blood flow during the second half of pregnancy, and test the hypothesis that foetal breathing movements (FBM) enhance this flow. Methods: Based on a power calculation, 110 women with low-risk singleton pregnancies were recruited to a longitudinal study that included three sets of observations during the second half of pregnancy. Ultrasound was used to determine inner diameter, peak systolic blood velocity and time-average maximum velocities in the SVC during rest and respiratory activity. Results: During the second half of pregnancy, SVC blood flow increased from 57.8 mL/min (95% CI 51.7-64.3) to 221.5 (204.5-239.3). Based on 558 sets of observations obtained during foetal rest and FBM, we found an overall increase in diameter from 0.41 cm (0.40-0.42) to 0.46 (0.44-0.48), peak systolic velocity from 35.9 cm/s (34.9-37.0) to 62.2 (59.1-65.5), and time-averaged maximum velocity from 20.3 cm/s (19.7-20.8) to 27.3 (26.1-28.6). This resulted in an overall 90% increase in mean SVC blood flow, from 108.1 mL/min (98.8-117.9) at rest to 205.9 (183.2-230.5) during FBM. Conclusion: The blood flow in the SVC increases during the second half of pregnancy and is substantially augmented during FBM. Since high-amplitude FBM additionally reduces flow in the inferior vena cava, the net effect is a prioritised venous drainage from the foetal head enhancing the washout of CO2 in that area, which also contains the chemoreceptors.

Please cite this paper as: Baghestan E, Irgens L, Bordahl P, Rasmussen S. Risk of recurrence and subsequent delivery after obstetric anal sphincter injuries. BJOG 2012;119:62–69. Objective To investigate the recurrence risk, the likelihood of having further deliveries and mode of delivery after third to fourth degree obstetric anal sphincter injuries (OASIS). Design Population-based cohort study. Setting The Medical Birth Registry of Norway. Population A cohort of 828 864 mothers with singleton, vertex-presenting infants, weighing 500 g or more, during the period 1967–2004. Methods Comparison of women with and without a history of OASIS with respect to the occurrence of OASIS, subsequent delivery rate and planned caesarean rate. Main outcome measures OASIS in second and third deliveries, subsequent delivery rate and mode of delivery. Results Adjusted odds ratios of the recurrence of OASIS in women with a history of OASIS in the first, and in both the first and second deliveries, were 4.2 (95% CI 3.9–4.5; 5.6%) and 10.6 (95% CI 6.2–18.1; 9.5%), respectively, relative to women without a history of OASIS. Instrumental deliveries, in particular forceps deliveries, birthweights of 3500 g or more and large maternity units were associated with a recurrence of OASIS. Instrumental delivery did not further increase the excess recurrence risk associated with high birthweight. A man who fathered a child whose delivery was complicated by OASIS was more likely to father another child whose delivery was complicated by OASIS in another woman who gave birth in the same maternity unit (adjusted OR 2.1; 95% CI 1.2–3.7; 5.6%). However, if the deliveries took place in different maternity units, the recurrence risk was not significantly increased (OR 1.3; 95% CI 0.8–2.1; 4.4%). The subsequent delivery rate was not different in women with and without previous OASIS, whereas women with a previous OASIS were more often scheduled to caesarean delivery. Conclusion Recurrence risks in second and third deliveries were high. A history of OASIS had little or no impact on the rates of subsequent deliveries. Women with previous OASIS were delivered more frequently by planned caesarean delivery.

OBJECTIVE: To assess whether premature rupture of membranes (PROM) is associated with placental abruption. DESIGN: Population-based study. SETTING: Data were extracted from the Medical Birth Registry of Norway. POPULATION: All women with PROM (18,889 cases), including 3,077 cases of preterm premature rupture of membranes (p-PROM), among a total of 355 416 singleton births in Norway during 1999-2005 with gestational age 17-44 weeks. METHODS: Logistic regression was used to assess whether placental abruption was associated with PROM in preterm and term births. MAIN OUTCOME MEASURES: Placental abruption. RESULTS: The occurrence of placental abruption in p-PROM was higher than in the total study population, 11.0 per 1,000 (34 of 3 077) vs. 4.2 per 1 000 (1 495 of 355 416; adjusted odds ratio 2.6, 95% confidence interval 1.8-3.7). Restricting the analyses to preterm births, the occurrence of placental abruption was less in p-PROM (11.0 per 1,000) than in births without p-PROM (36.1 per 1 000; adjusted odds ratio 0.3, 95% confidence interval 0.2-0.4). In term births, no statistically significant association was observed. CONCLUSIONS: The findings suggest that in p-PROM the risk of placental abruption is not higher than in other preterm births; rather the opposite. However, comparing the risks in p-PROM and the total gestational age range, the present study confirmed results reported in previous studies of a higher risk of placental abruption in p-PROM than in the total birth population.

Objective. To study the association between maternal weight gain in pregnancy and fetal abdominal circumference in the second trimester. Design. Prospective cross-sectional study. Setting. Low-risk antenatal clinic. Population. Six hundred and fifty women with low-risk pregnancy. Methods. Women with a regular menstrual period (28±4 days) and certain information on the last menstrual period were recruited when they were referred for routine ultrasound scanning. Women with a discrepancy of> 14 days between ultrasound and menstrual age were excluded. Maternal weight gain during pregnancy was derived from information in the antenatal chart and the weekly weight gain was calculated. Fetal abdominal circumference measurements were registered in gestational weeks 15-25 and their z-scores, together with the z-scores of maternal weight gain, were used in a linear regression analysis. Main outcome measures. Association between maternal weight gain and fetal abdominal circumference. Results. Based on the complete data of 515 women we found a mean maternal weight gain during pregnancy of 0.39kg/week and a positive association between this weight gain and fetal abdominal circumference in the second trimester (r=0.122 (95%CI 0.051-0.194)), with the strongest effect in women with the slowest weight gain (