Ultrasonic methods of predicting the estimated date of confinement.

The present study examines the relative accuracy of 2 ultrasonic methods of predicting the estimated date of confinement (EDC). The first technique, mean projected gestational age (MPGA), utilizes 2 fetal biparietal diameter (BPD) readings between 19 and 30 weeks' gestation with at least a 3-week interval between examinations. The 2 values are fitted to the mean of the standard curve as closely as possible and an EDC is predicted. The second method, growth adjusted sonographic age (GASA), is based on 1 BPD measurement in the second trimester and another in the third. The first is plotted on the mean and then readjusted depending on the percentile into which the second falls (below 25, 25 to 75, above 75). The EDC was blindly predicted in 120 patients, 60 by the MPGA method and 60 by the GASA technique. These were compared with 60 controls whose EDCs were predicted on the basis of excellent clinical dates. The interval between the predicted EDC and the actual delivery date was calculated for each patient and the results were compared. There was no statistical difference between the 2 techniques.