Prediction of the date of delivery based on first trimester ultrasound measurements: an independent method from estimated date of conception.

OBJECTIVE: We aimed to develop a population-based nomogram based on 1st trimester ultrasound examination as an independent predictor of the remaining days of pregnancy. METHODS: Fetal measurements were collected in singleton pregnancies undergoing first trimester examination. We prospectively collected actual date of delivery. Predictions of the median interval and key centiles from examination to delivery were computed using crown rump length (CRL), biparietal diameter (BPD), head circumference (HC), and abdominal circumference (AC) measurements. RESULTS: A total of 3738 examinations were included. We computed median and centiles for remaining days of pregnancies from the time of first trimester measurements. The prediction ability of CRL, HC, and BPD was not different but AC yielded worse results. About 90% of the births fell within 14 days of predicted day of delivery, with a median error of 6 days. CONCLUSION: We have developed a method to accurately predict date of delivery from the time of first trimester measurements. It allows monitoring fetal growth and pregnancies at term by considering the duration of pregnancy as a variable rather than a constant.