'Expert' analysis of menstrual and ultrasound data in pregnancy--gestational dating

The expected date of delivery (EDD) using a precise ultrasound day rule was compared with the scan EDD alone in 219 singleton pregnant women who were certain of their last menstrual period, and booked in the obstetric department of a district general hospital. The system compared the ultrasound biometric measurement with the normal range of a published chart of fetal size and, using the day rule concept, the final EDD selected by an 'expert' computer system. Statistical analysis using similar methods as in other published studies showed that the 'expert' system correlated with the actual date of the onset of spontaneous labour at least as well as scan dates alone. Menstrual data should not be rejected in favour of ultrasonic biometry in all cases and a computer system using a precise day rule should be a valuable addition to computerised maternity databases and ultrasound machines.