Prediction of the time of delivery by means of ultrasonic scanning between the 20th and 30th weeks of pregnancy
Hasch, E.; Lange, A.P.; Sørensen, T.
Acta Obstetricia et Gynecologica Scandinavica 58(5): 457-460
1979
ISSN/ISBN: 0001-6349 PMID: 532566 Document Number: 147367
Ultrasonic scanning, with measurement of the biparietal diameter, from the 20th-30th wk of pregnancy, was carried out on 738 women with an uncomplicated pregnancy and spontaneous delivery of a healthy child, weighing more than 2500 g. The time of delivery was calculated by a reference curve. Women [642] had a reliable calculated expected data of delivery, using information regarding the last menstrual period and clinical examination, but in 96 women this was considered as unknown or uncertain. The cumulative curve of the time of delivery determined by ultrasonic scanning, in relation to the actual time of delivery was similar for the 2 groups, as an expression of a reliable and independent measuring technique. Division into early and late timing of measurement showed no definite difference in the prediction. In the group of women with reliable dates, the calculated expected delivery date using biparietal diameter measurement, lay, on average, 5-6 days later. This can be explained by the difference in sound speed between the apparatus used to determine the reference curve and that employed for the present investigation. In the group with a reliable expected date of delivery, 92% gave birth within .+-. 14 days of term, as calculated from menstrual data, and 87% within .+-. 14 days of term as calculated from the biparietal diameter. In the group with uncertain dates, 83% gave birth within .+-. 14 days, in relation to the time of delivery calculated from ultrasonic scanning. It is possible with an acceptable margin of safety, to predict the time of delivery of a patient on the basis of a single measurement of the biparietal diameter from the 20th-30th wk of pregnancy. A measurement of the biparietal diameter at this time is of additional importance as the basal value, should the pregnancy be complicated later by the need for regular measurement of the biparietal diameter.