Objective: To assess the feasibility and accuracy of fetal sex identification during the first trimester ultrasound exam.
Methods: A prospective study was carried out on 312 fetuses at 11-14 weeks' gestation. The genital region was examined by transabdominal ultrasound. The angle of the genital tubercle to a horizontal line through the lumbosacral skin was measured. Fetal gender was assigned as male if this angle was > 30 degrees and female when it was < 10 degrees .
Results: Sex assignment was feasible in 89.7% and accurate in 85.7% of fetuses. Accuracy was similar in males as in females (87.9% vs 83.3%; NS). However, accuracy increased significantly during the gestational age period in male (Chi-square for trend P = 0.03) but not in female (P = 0.41) fetuses. Compared with singletons, presence of multiple fetuses (n = 12) did not influence feasibility or accuracy (89.2% vs 96% and 85.6% vs 86.4% respectively). In male fetuses, there was a significant increase in the angle of the genital tubercle with increasing crown-rump length(CRL) (r = 0.667; p = 0.025), while in females the angle did not significantly change with increasing gestation.
Conclusion: Sonographic first trimester sex assignment is highly feasible and accurate.