Use of multiplanar 3-dimensional ultrasonography for prenatal sex identification

Determination of fetal sex is an important part of detailed second-trimester ultrasonography. This task can be hindered by the fetal position, a low amniotic fluid volume, and advanced gestational age. Identification of fetal sex is further important in multiple gestations and prior histories of indeterminate-sex pregnancies. The goal of the study was to compare the effectiveness of 2-dimensional ultrasonography (2DUS) versus 3-dimensional ultrasonography (3DUS) at sex identification and to determine how genitalia measurements taken with 3DUS technology compare with measurements taken with 2DUS.

A total of 111 patients at or beyond 16 weeks' gestation were recruited. Assignments of fetal sex using 2DUS and 3DUS were compared by the test of proportions. The actual neonatal sex was obtained after delivery. Given such small number of misdiagnoses by either 2DUS or 3DUS, the accuracies of the two modalities were not found to be statistically distinguishable from one another (P = .5585). The penile length, scrotal width, and bilabial diameter according to gestational age were measured and compared with previously published 2DUS data by t tests.

Sexes were assigned and interpreted in 65 cases. Ranges of genitalia measurements were plotted against gestational age and were found to be comparable with published data. There was a dramatic difference between the bilabial diameter and scrotal width with advancing gestational age that made sex determination much easier in the third trimester.

Although 3DUS did not have better prediction of fetal sex when compared with 2DUS, it may be a useful tool in conjunction with traditional imaging techniques in assigning fetal sex.