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Background: Children with low-income parents have a higher risk of mental disorders, although it is unclear whether other parental characteristics or genetic confounding explain these associations and whether it is true for all mental disorders., Methods: In this registry-based study of all children in Norway (n = 1 354 393) aged 5-17 years from 2008 to 2016, we examined whether parental income was associated with childhood diagnoses of mental disorders identified through national registries from primary healthcare, hospitalizations and specialist outpatient services., Results: There were substantial differences in mental disorders by parental income, except for eating disorders in girls. In the bottom 1% of parental income, 16.9% [95% confidence interval (CI): 15.6, 18.3] of boys had a mental disorder compared with 4.1% (95% CI: 3.3, 4.8) in the top 1%. Among girls, there were 14.2% (95% CI: 12.9, 15.5) in the lowest, compared with 3.2% (95% CI: 2.5, 3.9) in the highest parental-income percentile. Differences were mainly attributable to attention-deficit hyperactivity disorder in boys and anxiety and depression in girls. There were more mental disorders in children whose parents had mental disorders or low education, or lived in separate households. Still, parental income remained associated with children's mental disorders after accounting for parents' mental disorders and other factors, and associations were also present among adopted children., Conclusions: Mental disorders were 3- to 4-fold more prevalent in children with parents in the lowest compared with the highest income percentiles. Parents' own mental disorders, other socio-demographic factors and genetic confounding did not fully explain these associations., (© The Author(s) 2021. Published by Oxford University Press on behalf of the International Epidemiological Association.)

Genetic liability for schizophrenia is associated with psychopathology in early life. It is not clear if these associations are time dependent during childhood, nor if they are specific across different forms of psychopathology. Using genotype and questionnaire data on children (N = 15 105) from the Norwegian Mother, Father and Child Cohort Study, we used schizophrenia polygenic risk scores to test developmental stability in associations with measures of emotional and behavioral problems between 18 months and 5 years, and domain specificity in associations with symptoms of depression, anxiety, conduct problems, oppositionality, inattention, and hyperactivity at 8 years. We then sought to identify symptom profiles-across development and domains-associated with schizophrenia polygenic liability. We found evidence for developmental stability in associations between schizophrenia polygenic risk scores and emotional and behavioral problems, with the latter being mediated specifically via the rate of change in symptoms (β slope = 0.032; 95% CI: 0.007-0.057). At age 8, associations were better explained by a model of symptom-specific polygenic effects rather than effects mediated via a general psychopathology factor or by domain-specific factors. Overall, individuals with higher schizophrenia polygenic risk scores were more likely (OR = 1.310 [95% CIs: 1.122-1.528]) to have a profile of increasing behavioral and emotional symptoms in early childhood, followed by elevated symptoms of conduct disorder, oppositionality, hyperactivity, and inattention by age 8. Schizophrenia-associated alleles are linked to specific patterns of early-life psychopathology. The associations are small, but findings of this nature can help us better understand the developmental emergence of schizophrenia., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Background: A link between suboptimal fetal growth and higher risk of cardiovascular disease (CVD) is well documented. It has been difficult to assess the contribution of environmental versus genetic factors to the association, as these factors are closely connected in nuclear families. We investigated the association between offspring birthweight and CVD mortality in parents, aunts and uncles, and examined whether these associations are explained by CVD risk factors., Methods: We linked Norwegian data from the Medical Birth Registry, the Cause of Death Registry and cardiovascular surveys. A total of 1 353 956 births (1967-2012) were linked to parents and one maternal and one paternal aunt/uncle. Offspring birthweight and CVD mortality association among all relationships was assessed by hazard ratios (HR) from Cox regressions. The influence of CVD risk factors on the associations was examined in a subgroup., Results: Offspring birthweight was inversely associated with CVD mortality among parents and aunts/uncles. HR of CVD mortality for one standard deviation (SD) increase in offspring birthweight was 0.72 (0.69-0.75) in mothers and 0.89 (0.86-0.92) in fathers. In aunts/uncles, the HRs were between 0.90 (0.86-0.95) and 0.93 (0.91-0.95). Adjustment for CVD risk factors in a subgroup attenuated all the associations., Conclusions: Birthweight was associated with increased risk of CVD in parents and in aunts/uncles. These associations were largely explained by CVD risk factors. Our findings suggest that associations between offspring birthweight and CVD in adult relatives involve both behavioural variables (especially smoking) and shared genetics relating to established CVD risk factors., (© The Author(s) 2019. Published by Oxford University Press on behalf of the International Epidemiological Association.)

Background: Maternal alcohol use during pregnancy has repeatedly been associated with development of attention-deficit hyperactivity disorder (ADHD) in the offspring. It is, however not known whether this reflects a direct casual intra-uterine effect or a non-causal relationship due to confounding. We used three different approaches to control for measured and unmeasured confounding: statistical adjustment for covariates, negative control comparison against maternal pre-pregnancy alcohol use, and comparison among differentially exposed siblings., Methods: The sample comprised 114 247 children (34 283 siblings) from 94 907 mothers, recruited to the Norwegian Mother and Child Birth Cohort Study between 1999 and 2008. Self-reported measurements of alcohol use were obtained in week 30 during the pregnancy. Mothers rated offspring ADHD symptoms at 5 years on two measures. Clinical ADHD diagnoses were obtained from the Norwegian Patient Registry., Results: We found an overall positive association between maternal alcohol use during pregnancy and offspring ADHD symptoms, which was only marginally attenuated after inclusion of measured covariates. Both the negative control and the sibling comparison analysis further attenuated the estimated association, but it remained greater than zero [β = 0.017, 95% confidence interval (CI) = 0.005-0.030). No association was found between maternal alcohol use during pregnancy and offspring ADHD diagnosis., Conclusions: For offspring ADHD symptoms we found a weak, but possibly causal association with maternal alcohol use during pregnancy, but no such effect was observed for clinical ADHD diagnosis., (© The Author 2017; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association)

Background: The positive association between caesarean section (CS) and autism spectrum disorder (ASD) may be attributed to preterm delivery. However, due to lack of statistical power, no previous study thoroughly examined this association across gestational age. Moreover, most studies did not differentiate between emergency and planned CS., Methods: Using population-based registries of four Nordic countries and Western Australia, our study population included 4 987 390 singletons surviving their first year of life, which included 671 646 CS deliveries and 31 073 ASD children. We used logistic regression to estimate odds ratios (OR) and their 95% confidence intervals (CI) for CS, adjusted for gestational age, site, maternal age and birth year. Stratified analyses were conducted by both gestational age subgroups and by week of gestation. We compared emergency versus planned CS to investigate their potential difference in the risk of ASD., Results: Compared with vaginal delivery, the overall adjusted OR for ASD in CS delivery was 1.26 (95% CI 1.22-1.30). Stratified ORs were 1.25 (1.15-1.37), 1.16 (1.09-1.23), 1.34 (1.28-1.40) and 1.17 (1.04-1.30) for subgroups of gestational weeks 26-36, 37-38, 39-41 and 42-44, respectively. CS was significantly associated with risk of ASD for each week of gestation, from week 36 to 42, consistently across study sites (OR ranged 1.16-1.38). There was no statistically significant difference between emergency and planned CS in the risk of ASD., Conclusion: Across the five countries, emergency or planned CS is consistently associated with a modest increased risk of ASD from gestational weeks 36 to 42 when compared with vaginal delivery., (© The Author 2016; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association)

Background: Gulf War veterans (GWVs) have an elevated risk of reporting symptoms of mental disorders as compared with nondeployed military controls. A difficulty in the Gulf War health research is that most health outcomes are self-reported; therefore, it is highly relevant to study objective outcomes in this line of research. The Danish National Prescription Registry provides an opportunity to use the prescription of drugs as an objective evaluation of the impact of mental health disorders at the individual level. In this study, we investigated the prescription of drugs and postdeployment hospitalizations for mental disorders among GWVs compared with a control population of nonveterans (NVs)., Methods: A prospective registry study including a cohort of 721 GWVs and a control cohort of 3,629 NVs. Main outcome measures were incidence of (1) use of antidepressants, (2) use of anxiolytic/hypnotic medication, and (3) number of postdeployment psychiatric contacts. The association between outcomes and GWVs status was studied by using time-to-event analysis. The index date was the return date from the last deployment to the Gulf. The follow-up period was the time from index date until December 31, 2014., Findings: GWVs had an elevated average risk over time for use of both types of medication compared with NV. For use of antidepressants the average hazard rate (HR) was 2.56, with 95% confidence interval (CI) = 2.04-3.21 (p < 0.0001); for use of anxiolytic/hypnotic medication the corresponding results were HR = 1.78, CI = 1.37-2.31 (p < 0.0001). The interaction with time was statistically significant with HR increasing with time for both outcomes. Incident use of antidepressants in GWVs after 10 years was two times higher than among NV, after 20 years it was nearly four times higher than among NV. Incident use of anxiolytic/hypnotic medication was one and a half that of NV after 10 years, but nearly three times that of NV after 20 years. There was no difference in rate of postdeployment psychiatric contacts., Discussion/impact/recommendations: The findings of increased use of antidepressants and anxiolytic or hypnotic medicine among GWVs compared with NVs were rather surprising since we recently, by using the same study population, found that deployment to the Persian Gulf was not associated with increased sickness absence or reduced labor market attachment. However, our results indicate that the mental health of the Danish GWVs is worse than in NV, and that this unfavorable difference increased with time. A possible explanation is that veterans have a high motivation for being in work, and that the deployment-related mental problems they may have acquired do not impair their ability to work, when treated properly. Furthermore, registry-based research in GWVs could include other outcomes, e.g., the use of pain medication, and other military comparison groups, e.g., veterans deployed to other areas than the Persian Gulf in addition to NV. The method of surveillance of military personnel with register data pertinent to health and monitoring outcomes compared with suitable control populations is highly recommended as a tool in the prevention of deployment-related health problems., (Reprint & Copyright © 2017 Association of Military Surgeons of the U.S.)

Objective: To examine the assumption that postdeployment incidence of sickness and other absence from work are higher among Gulf War Veterans compared with nonveterans., Methods: A prospective registry study including a cohort of 721 Danish Gulf War Veterans and a control cohort of 3,629 nonveterans selected from the general Danish population. Outcome measures were up to 23 years postdeployment incidence of (1) long-term sickness absence and (2) long-term all types of absence from work. Long term with regard to sickness and other absence was defined as exceeding 8 weeks. The association between outcomes and information on deployment history was studied using time-to-event analysis. The index date was the return date from the last deployment to the Gulf. The follow-up period was the time from index date until April 27, 2014., Results: As the main finding, no difference was found between veterans and nonveterans in the incidence rate of long-term sickness absence. After an initial short period (3 months) with elevated incidence rate of long-term absence from work among veterans, there was no difference between the cohorts., Conclusion: Among Danish Gulf War Veterans, no postdeployment increased risk of long-term sickness absence or long-term absence from work was found as compared with nonveterans., (Reprint & Copyright © 2016 Association of Military Surgeons of the U.S.)

This is an update of the Norwegian Mother and Child Cohort Study (MoBa) cohort profile which was published in 2006. Pregnant women attending a routine ultrasound examination were initially invited. The first child was born in October 1999 and the last in July 2009. The participation rate was 41%. The cohort includes more than 114 000 children, 95 000 mothers and 75 000 fathers. About 1900 pairs of twins have been born. There are approximately 16 400 women who participate with more than one pregnancy. Blood samples were obtained from both parents during pregnancy and from mothers and children (umbilical cord) after birth. Samples of DNA, RNA, whole blood, plasma and urine are stored in a biobank. During pregnancy, the mother responded to three questionnaires and the father to one. After birth, questionnaires were sent out when the child was 6 months, 18 months and 3 years old. Several sub-projects have selected participants for in-depth clinical assessment and exposure measures. The purpose of this update is to explain and describe new additions to the data collection, including questionnaires at 5, 7, 8 and 13 years as well as linkages to health registries, and to point to some findings and new areas of research. Further information can be found at [www.fhi.no/moba-en]. Researchers interested in collaboration and access to the data can complete an electronic application available on the MoBa website above., (© The Author 2016; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association.)

Background: Research studies exploring the determinants of disease require sufficient statistical power to detect meaningful effects. Sample size is often increased through centralized pooling of disparately located datasets, though ethical, privacy and data ownership issues can often hamper this process. Methods that facilitate the sharing of research data that are sympathetic with these issues and which allow flexible and detailed statistical analyses are therefore in critical need. We have created a software platform for the Virtual Pooling and Analysis of Research data (ViPAR), which employs free and open source methods to provide researchers with a web-based platform to analyse datasets housed in disparate locations., Methods: Database federation permits controlled access to remotely located datasets from a central location. The Secure Shell protocol allows data to be securely exchanged between devices over an insecure network. ViPAR combines these free technologies into a solution that facilitates 'virtual pooling' where data can be temporarily pooled into computer memory and made available for analysis without the need for permanent central storage., Results: Within the ViPAR infrastructure, remote sites manage their own harmonized research dataset in a database hosted at their site, while a central server hosts the data federation component and a secure analysis portal. When an analysis is initiated, requested data are retrieved from each remote site and virtually pooled at the central site. The data are then analysed by statistical software and, on completion, results of the analysis are returned to the user and the virtually pooled data are removed from memory., Conclusions: ViPAR is a secure, flexible and powerful analysis platform built on open source technology that is currently in use by large international consortia, and is made publicly available at [http://bioinformatics.childhealthresearch.org.au/software/vipar/]., (© The Author 2015. Published by Oxford University Press on behalf of the International Epidemiological Association.)

Background: Immigrants to Europe account for a significant proportion of births in a context of rising caesarean rates. We examined the risk of planned and emergency caesarean section (CS) by immigrants' length of residence in Norway, and compared the results with those of non-immigrants., Methods: We linked population-based birth registry data to immigration data for first deliveries among 23 147 immigrants from 10 countries and 385 306 non-immigrants between 1990-2009. Countries were grouped as having low CS levels (<16%; Iraq, Pakistan, Poland, Turkey, Yugoslavia, Vietnam) or high CS levels (>22%; the Philippines, Somalia, Sri Lanka, Thailand). Associations between length of residence and planned/emergency CS were estimated as relative risks (RR) with 95% confidence intervals (CI) in multivariable models., Results: In the immigrant group with low CS levels, planned, but not emergency, CS was independently associated with longer length of residence. Compared with recent immigrants (<1 year), the risk of planned CS was 70% greater among immigrants with residency of 2-5 years (RR 1.70, CI: 1.19-2.42), and twice as high in those with residency of ≥ 6 years. (RR 2.01, CI: 1.28-3.17). Compared with non-immigrants, immigrants in the low group with residency <2 years had lower risk of planned CS, while those with residency >2 years had greater risk of emergency CS. In the high group, the risk of planned CS was similar to non-immigrants, while emergency CS was 51-75% higher irrespective of length of residency., Conclusion: Efforts to improve immigrants' labour outcomes should target subgroups with sustained high emergency caesarean risk., (© The Author 2014. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.)

Aims: Cardiovascular diseases (CVDs) have been related to low birth weight, suggesting the foetal environment may program future risk. Alternatively, common genetic factors for both low birth weight and CVD could explain such associations. We investigated associations between offspring birth weight and paternal and maternal cardiovascular mortality and offspring birth weight and cardiovascular mortality among all four grandparents, and further assessed the mediating role of maternal smoking during pregnancy., Methods and Results: All births from 1967 to 2008 that could be linked to parents and grandparents comprised the population (n = 1,004,255). The mortality follow-up among parents was from 1970 to 2008 and among grandparents from 1960 to 2008. The association of grandparental mortality with maternal smoking during pregnancy was analysed in a subpopulation of those born after 1997 (n = 345,624). Per quintile higher in birth weight was related to 0.82 (0.75-0.89) hazard ratio from coronary heart disease in mothers and 0.94 (0.92-0.97) in fathers. For stroke, these were 0.85 (0.78-0.92) and 0.94 (0.89-1.00), respectively. In grandparents for cardiovascular causes, the effects were 0.95 (0.93-0.96) (maternal grandmother), 0.97 (0.96-0.98) (maternal grandfather), 0.96 (0.94-0.98) (paternal grandmother), and 0.98 (0.98-1.00) (paternal grandfather). Adjusting for maternal smoking in pregnancy in the subpopulation accounted for much of the effect on grandparental cardiovascular mortality in all categories of birth weight. For grandparental diabetes mortality, U-shaped associations were seen with grandchild birth weight for the maternal grandmother and inverse associations for all other grandparents., Conclusion: Associations between CVD mortality in all four grandparents and grandchild birth weight exist, and while genetic and environmental factors may contribute to these, it appears that there is an important role for maternal smoking during pregnancy (and associated paternal smoking) in generating these associations. For diabetes, however, it appears that intrauterine environmental influences and genetic factors contribute to the transgenerational associations.

Study Objective: We compared sleep problems during pregnancy and sleep dissatisfaction 18 months after pregnancy in pregnant women with binge eating disorder (BED) symptoms and pregnant women without an eating disorder., Design: Norwegian Mother and Child Cohort Study (MoBa)., Patients or Participants: Data were gathered from 72,435 women. A total of 1,495 (2.1%) women reported having BED symptoms both before and during pregnancy; 921 (1.3%) reported pre-pregnancy BED symptoms that remitted during pregnancy; 1,235 (1.7%) reported incident BED symptoms during pregnancy; and 68,784 (95.0%) reported no eating disorder symptoms before or during pregnancy (referent)., Measurements and Results: Questionnaires were collected at 3 time points, with a median completion time of 17.1 weeks gestation, 30.1 weeks gestation, and 18.7 months after childbirth. We collected information on demographics, eating disorder status before and during pregnancy, sleep problems during the first 18 weeks of pregnancy, hours of sleep during the third trimester, and sleep satisfaction 18 months after childbirth. All BED symptom groups were significantly more likely to report sleep problems during the first 18 weeks of pregnancy than the referent (adjusted odds ratio [OR] = 1.26-1.42, false discovery rate [FDR] P < 0.05). In the third trimester, women with incident BED symptoms during pregnancy were more likely to report more hours of sleep than the referent (adjusted OR = 1.49, FDR P < 0.01). All BED symptom groups had higher odds of reporting more dissatisfaction with sleep 18 months after childbirth (adjusted ORs = 1.28-1.47, FDR P < 0.01)., Conclusions: BED before or during pregnancy is associated with sleeping problems during pregnancy and dissatisfaction with sleep 18 months after childbirth. Health care professionals should inquire about BED during pregnancy as it may be associated with sleep disturbances, in addition to the hallmark eating concerns.

Background: The risk of pre-eclampsia is reduced for second and later births. The causes and mechanisms behind this reduction are unknown. The aim of the study was to estimate the risk of pre-eclampsia in primiparous women according to history of spontaneous and induced abortions, while controlling for several potentially confounding factors., Methods: The sample consisted of 20 846 primiparous women participating in the Norwegian Mother and Child Cohort Study (MoBa). Information on abortions and confounders were self-reported in postal questionnaires. The diagnosis of pre-eclampsia was retrieved from the Medical Birth Registry of Norway. Estimation and confounder control was performed with multiple, logistic regression., Results: One previous induced abortion reduced the risk moderately [odds ratio (OR) 0.84, 95% confidence interval (CI) 0.69-1.02]. Two or more induced abortions reduced the risk more significantly (OR 0.36, 95% CI 0.18-0.73). Adjustment for confounders did not change the estimates., Conclusions: The protective effect of two prior induced abortions was similar to what is commonly seen after one birth. Spontaneous abortions may to a larger extent than induced abortions be associated with other factors, such as infertility, that may increase the risk of pre-eclampsia. Normal pregnancies interrupted in early pregnancy may induce immunological changes that reduce the risk of pre-eclampsia in a subsequent pregnancy.

Background: We recently reported increased social inequality for post-neonatal death. The aim of the present study was to investigate the association between socioeconomic status and cause-specific post-neonatal death., Methods: All 1,483,857 live births recorded in the Medical Birth Registry of Norway from 1969-95 with information on parents' education were included. During the post-neonatal period (from 28 to 364 days of life) 4,464 infants died. Differences between education groups were estimated as risk differences, relative risks, population attributable fractions, and relative index of inequality., Results: The major causes of death were congenital conditions, sudden infant death syndrome (SIDS), and infections. Post-neonatal mortality declined from 3.2/1,000 in the 1970s to 1.9/1,000 in the 1990s, mainly due to reduced mortality from congenital conditions. The absolute risk for SIDS increased by 0.51/1,000 in the same period among infants whose mothers had low education, while it decreased by 0.56/1,000 for those whose mothers had high education. The relative risk for SIDS among infants whose mothers had low education increased from 1.02 in the 1970s to 2.39 in the 1980s and 5.63 in the 1990s. Among infants whose fathers were not recorded in the Birth Registry, the absolute risk of SIDS increased by 0.79/1,000 from the 1970s to the 1990s., Conclusions: Increased social inequality for post-neonatal death was primarily due to increases in the absolute and relative risks of SIDS among infants whose mothers have low education. Social inequality widened during the study period for SIDS and deaths caused by infections.

Background: The aim of this study was to examine the association between socioeconomic status and risk of infant death in Norway from 1967 to 1998., Methods: Information from the Medical Birth Registry of Norway on all live births and infant deaths was linked to information from Statistics Norway on parents' education. There were 1777364 eligible live births and 15517 infant deaths. Differences between education groups were estimated as risk differences, relative risks, population attributable fractions, and index of inequality ratios., Results: The risk of infant death decreased in all education groups, and the level of education increased over time. The trends differed for neonatal and postneonatal death. For neonatal death the risk difference between infants whose mothers had high and low education was reduced from 3.5/1000 in the 1970s to 0.9/1000 in the 1990s. The relative index of inequality (RII) for maternal education decreased from 1.72 to1.32. The proportion of neonatal deaths that could be attributed to <13 years of education decreased from 22.3 to 8.4. For postneonatal death the risk difference between infants whose mothers had high and low education increased from 0.7/1000 in the 1970s to 2.0/1000 in the 1990s. The RII for maternal education increased from 1.31 to 4.00. The population attributable fraction increased from 9.7 to 39.5., Conclusions: An inverse association between socioeconomic status and risk of postneonatal death persists, albeit there was a considerable reduction in risk between 1967 and 1998.

Background: Mother's ethnicity is associated with her baby's birthweight and risk of perinatal mortality. Given the close relation between birthweight and perinatal mortality, we explored whether ethnic differences in birthweight explain ethnic differences in perinatal mortality., Methods: Data on all births to mothers born in Norway (808 658), Pakistan (6854), Vietnam (3283) and North Africa (1461) from 1980 to 1995 were obtained from the Medical Birth Registry of Norway. The associations between birthweight and perinatal mortality among ethnic groups were analysed using univariate and multivariate methods., Results: Mean birthweights were low for Vietnamese and Pakistani mothers (3202 g, 3244 g) and high for Norwegian and North African mothers (3530 g, 3559 g). Mean birthweights were largely unrelated to perinatal mortality, which was lowest for Vietnamese (8.2/1000, 95% CI: 5.1-11.3) and highest for Pakistanis (14.9/1000, 95% CI: 12.0-17.7). Intermediate perinatal mortality rates were found among Norwegians (9.5/1000, 95% CI: 9.3-9.7) and North Africans (9.6/1000, 95% CI: 4.6-14.6). Further comparison of weight-specific mortality rates between the two largest ethnic groups showed the low birthweight paradox, where among low-weight births, perinatal mortality was lower among Pakistani than among Norwegian babies. However, adjustment to a relative birthweight scale (units of standard deviations from population-specific mean value) revealed higher rates of weight-specific mortality among Pakistanis across the entire range of birthweights. Multivariate adjustment for relative birthweight and other factors did not change these results., Conclusions: Differences in perinatal mortality between the ethnic groups were not explained by differences in mean birthweight. Paradoxical differences in birthweight-specific mortality rates could be resolved by adjustment to a relative scale.

To analyze the influence of consanguinity and maternal education on stillbirth and infant death for children born in Norway between 1967 and 1993, the authors studied 7,274 children of ethnic Pakistani origin and 1,431,055 children of Norwegian ethnic origin. Of these children, 31.0% of the Pakistani children and 0.1% of the Norwegian children had parents who were first cousins. Consanguinity increased the relative risk of stillbirth (odds ratio (OR) = 1.3, 95% confidence interval (CI) 1.0-1.6) and infant death (OR = 2.4, 95% CI 2.0-3.0), after adjustment for maternal education, maternal age, parity, and year of birth. In 1985-1993, 29% (95% CI 13-45) of stillbirths and infant deaths among the Pakistani group were attributable to consanguinity. In the Norwegian group, 17% (95% CI 13-21) of the deaths were attributable to factors associated with low maternal education, while in the Pakistani group, the corresponding estimate was nonsignificant. The risks of stillbirth and infant death were similar for children with non-consanguineous parents in both populations. This is an important observation considering the differences in socioeconomic status between the two groups. The authors conclude that consanguinity influenced stillbirth and infant death independent of maternal education, and that a large proportion of deaths could be attributed to consanguinity in the Pakistani group due to high frequencies of consanguinity.

The study compares frequencies of birth defects between immigrant groups and the rest of the Norwegian population in Norway and estimates the influence of consanguinity and socioeconomic factors on these frequencies. The authors studied all 1.56 million births in Norway from 1967 to 1993. Of these, 7,494 children had two Pakistani parents, 84,688 had one Norwegian and one immigrant parent, and 25,891 had two immigrant parents from countries other than Pakistan. The risk of birth defects relative to the Norwegian group was 0.98 (95% confidence interval 0.92-1.03) in the group with one foreign and one Norwegian parent, 1.39 (95% confidence interval 1.22-1.60) in the group with two Pakistani parents, and 1.04 (95% confidence interval 0.95-1.14) in the group with two parents from other foreign countries; 0.1% of the Norwegian and 30.1% of the Pakistani children had parents who were first cousins. There was no difference in risk between children of nonconsanguineous Pakistani parents and the other groups. The relative risk of birth defects among children whose parents were first cousins was about 2 in all groups. Among the Pakistani, 28% of all birth defects could be attributed to consanguinity. Low paternal educational level was associated with a slightly increased risk in the Norwegian group, while independent effects of parental educational levels were not found in any other groups.