Early-second-trimester fetal sex determination with ultrasound.

A prospective investigation was performed to determine the accuracy of fetal gender determination with ultrasound at 13-19 weeks' gestation. A determination could be made in 91 of 100 women. Factors associated with nonvisualization were maternal obesity and breech presentation. The findings on ultrasound were compared with phenotypic sex after birth. The overall accuracy of sex prediction was 92.3%; for males it was 89.5% and for females, 97.1%. Significantly fewer errors were noted as experience with gender identification increased.