Second trimester biparietal diameter size and the risk of adverse pregnancy outcomes

To identify the relationship between biparietal diameter (BPD) in the second trimester and adverse pregnancy outcomes in low-risk pregnancies.

This prospective cohort study was performed on 2219 singleton pregnant women from August 2008 to March 2010. The gestational age-specific percentiles of BPD at 17 to 24 weeks of gestation were established to categorize participants into three groups: a BPD < 10th percentile as small BPD, between 10th and 90th percentile as normal BPD and > 90th percentile as large BPD. Using logistic regression analysis, the association between BPD < 10th and > 90th percentile with pregnancy outcomes was evaluated after controlling for confounding factors.

There was a significantly increased risk of macrosomia [odds ratio (OR(adj)) = 2.1; 95% confidence intervals (CI), 1.23-3.78] and preterm labor (PTL) (OR(adj) = 1.9; 95% CI, 1.19-3.05) in fetuses with a BPD > 90th percentile compared with fetuses with a normal BPD, and there was a significant relationship between small for gestational age (SGA) at delivery and a BPD < 10th percentile at the second trimester (OR(adj) = 2.4; 95% CI, 1.77-3.52). No association was present between preeclampsia and second trimester BPD.

BPD in the first half of pregnancy is related to fetal size at term and risk of PTL.