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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.

Objectives The aims of the present study were to establish improved reference charts for growth of the fetal head, abdomen and femur, and to determine the effect of fetal and maternal factors. Study design This prospective longitudinal study included 650 low-risk pregnancies. Outer–outer biparietal diameter (BPD), head circumference (HC), mean abdominal diameter (MAD), abdominal circumference (AC) and femur length (FL) were measured by ultrasound, and the statistical analysis was based on regression analysis and multilevel modeling. Results Reference percentiles for the growth of MAD, AC and FL showed continuous growth in gestational week 10–40, while BPD and HC showed a slightly blunted growth toward the end of pregnancy. FL was the only variable that was not influenced by gender. There was a significant negative association between breech presentation and all five biometrical variables, while maternal weight was positively associated with all five variables. Cephalic index significantly influenced BPD and HC. Maternal height had a positive effect on BPD, HC, AC and FL, and parity had a positive effect on MAD and AC, while smoking influenced negatively HC, MAD, and FL. Terms for calculating conditional reference values and customisation for individualised growth assessment are presented. Conclusions New reference charts for the growth of fetal head, abdomen and femur are suggested for assessing fetal size and growth, and can be adjusted for maternal and fetal factors to suite individual pregnancies.