Sonographic dating of pregnancies among women with menstrual irregularities.

In order to study the benefit of sonographic dating, 277 women with irregular periods and 264 women with a scanty last bleeding had gestational age and estimated day of delivery (EDD) estimated from both last menstrual period (LMP) and measurement of fetal Biparietal Diameter (BPD) in the second trimester. For the women with irregular periods, the two estimates differed by more than 7 days for 51.6%, and more than 14 days for 25.6%. Corresponding figures for women with a scanty last bleeding were 44.3% and 21.6%, respectively. In general, the BPD estimates were better than the LMP estimates (P = less than 0.001) in predicting day of delivery, especially when the differences between the estimates exceeded 7 days. For women with irregular periods, post-term pregnancies decreased, from 20.2% according to the LMP estimate to 2.5% according to the BPD estimate. Corresponding figures for women with a scanty last bleeding were 16.7% and 4.5%, respectively. According to the LMP estimate, 64.8% of the women with irregular periods and 69.3% of the women with a scanty last bleeding gave birth within +/- 14 days of EDD. Corresponding figures for the BPD estimate were 83.6% and 88.3%, respectively. The conclusion is that sonographic dating of pregnancies among women with irregular periods and women with a scanty last bleeding substantially improve the accuracy of term prediction.