Fetal outcome when the ultrasound estimate of the day of delivery is more than 14 days later than the last menstrual period estimate

Objective To evaluate the effect on fetal outcome of changing the estimated day of delivery as calculated according to ultrasound measurements more th an 14 days later than the day estimated according to the last menstrual per iod. Design A non-selected population comprising 15 241 women was evaluated. A s tudy group (the day of delivery bared on the ultrasound estimate being chan ged to more than 14 days laser than the estimate based on the last menstrua l period) and a control group (the two estimates being within 7 days of eac h other) were compared regarding various parameters concerning fetal outcom e. Results Changing the estimated day of delivery, based on the ultrasound eva luation, to a date 14 days Inter than the day of delivery as estimated acco rding to the last menstrual period did not influence the risk of abortion, perinatal death or transferral to the neonatal intensive care unit. There w as a difference of 3 days in the accuracy of the prediction of day of deliv ery between the two groups. There rc,as a greater number of infants with a birth weight below 2500 g in the study group, but no difference was found b etween the groups in the number of infants with a birth weight < 2 SD from the mean according to the ultrasound estimate. Conclusion There was no indication of any adverse consequence of the routin e scan and change of estimated day of delivery among 15 000 pregnancies in a non-selected population.