[The value of estimating fetal age by means of ultrasound]

The authors estimated in 1,000 women the length of gestation using two criteria: the date of the last menstruation and the results of ultrasonic examination (ovarian sac and biparietal diameters). The women were allocated to one of four groups according to the details of their menstrual history: (1) last periods specified precisely, 28 +/- 5 days ; (2) last periods specified precisely, with longer or shorter cycles; (3) last periods doubtful, or (4) last periods unknown. An additional subdivision was made according to the foetal age at the time of the estimation. Statistical analysis showed that the average length of pregnancy measured by ultrasound was similar in all groups and series; only the standard deviation increased slightly towards the end of pregnancy. The results were similar to those obtained by estimating the length of gestation from the date of ovulation.