Screening for fetal spina bifida by ultrasound examination in the first trimester of pregnancy using fetal biparietal diameter.

Objective: Prenatal screening for aneuploidies is best achieved in the first trimester when there is no reliable screening test for spina bifida. Early ultrasound features may be too complex for routine screening. We assessed screening potential of simple and reproducible fetal biometric measurements at 11-14 weeks of gestation.

Study Design: A total of 34,951 unselected consecutive pregnancies included 18 with spina bifida. Another 28 cases were referred for assessment. Biometric measurements were expressed in multiples of the median for crown-rump length.

Results: Biparietal diameter (BPD) was smaller in spina bifida (P < .0001). In all, 22 of 44 (50%) cases with spina bifida aperta had a BPD <5th centile. BPD was independent of maternal adiposity and smoking status.

Conclusion: Simple and reproducible BPD at 11-14 weeks of gestation could detect half the cases of open fetal spina bifida by identifying 5% of pregnancies for expert scanning in first- and second-trimester examinations of the fetal spine and cranium.