To determine fetal growth in low risk pregnancies at the beginning of the third trimester and to assess the relative importance of fetal gender and maternal parity.Setting
Dutch primary care midwifery practice.Study design
Retrospective cohort study on 3641 singleton pregnancies seen at a primary care midwifery center in the Netherlands. Parameters used for analysis were fetal abdominal circumference (AC), fetal head circumference (HC), gestational age, fetal gender and maternal parity. Regression analysis was applied to describe variation in AC and HC with gestational age. Means and standard deviations in the present population were compared with commonly used reference charts. Multiple regression analysis was applied to examine whether gender and parity should be taken into account.Results
The fetal AC and HC increased significantly between the 27th and the 33rd week of pregnancy (AC r2 = 0.3652, P<0.0001; HC r2 = 0.3301, P<0.0001). Compared to some curves, our means and standard deviations were significantly smaller (at 30 + 0 weeks AC mean = 258 ±13 mm; HC mean = 281 ± 14 mm), but corresponded well with other curves. Fetal gender was a significant determinant for both AC (P<0.0001) and HC (P<0.0001). Parity contributed significantly to AC only but the difference was small (β = 0.00464).Conclusion
At the begining of the third trimester, fetal size is associated with fetal gender and, to a lesser extent, with parity. Some fetal growth charts (e.g., Chitty et al.) are more suitable for the low-risk population in the Netherlands than others.