Fetal sex determination by ultrasound scan in the second and third trimesters.

Sector real-time ultrasound examinations of the fetal perineal area were done on fetuses ranging in age from 14 weeks to term. An attempt was made to determine fetal sex in 404 consecutive cases. Seventeen cases were lost to follow-up and 20 fetuses under 16 weeks of age were omitted, as only two predictions were made in this group. The fetal sex was predicted in 266 of the remaining 367 fetuses with 93% accuracy. In this series, 194 fetuses were less than 24 weeks of age; within this group, 118 predictions were made with an accuracy rate of 86%.