Sonar measurement of fetal crown-rump length as means of assessing maturity in first trimester of pregnancy.

A method is reported by which the "in utero" crown-rump length of the fetus may be determined by sonar in the first trimester of pregnancy. The accuracy of the technique was assessed by comparing the sonar and the direct postabortum measurements of fetuses in cases of missed abortion. A normal curve of fetal crown-rump length was derived from 214 examinations on 80 patients and by using these values in a further "blind" series it was found possible to predict the maturity of pregnancy to within three days, between the sixth and the 14th weeks of pregnancy.