Accuracy of fetal sex determination on ultrasound examination in the first trimester of pregnancy.

Purpose: The aim of this study was to evaluate the feasibility and success rate of sex determination on transabdominal sonographic examination at 11-13 weeks' gestation and to identify factors influencing accuracy.

Methods: In this prospective observational evaluation of 672 fetuses between 11 weeks' and 13 weeks + 6 days' gestational age (GA), we determined fetal sex according to the angle of the genital tubercle viewed on the midsagittal plane. We also analyzed maternal, fetal, and operator factors possibly influencing the accuracy of the determination.

Results: Fetal sex determination was feasible in 608 of the 672 fetuses (90.5%), and the prediction was correct in 532 of those 608 cases (87.5%). Fetal sex was more accurately predicted as the fetal crown-rump length (CRL), and GA increased and was less accurately predicted as the maternal body mass index increased. A CRL greater than 55.7 mm, a GA more than 12 weeks + 2 days, and a body mass index below 23.8 were identified as the best cutoff values for sex prediction. None of the other analyzed factors influenced the feasibility or accuracy of sex determination.

Conclusions: The sex of a fetus can be accurately determined on sonographic examination in the first trimester of pregnancy; the accuracy of this prediction is influenced by the fetal CRL and GA and by the maternal body mass index. © 2015 Wiley Periodicals, Inc. J Clin Ultrasound 44:272-277, 2016.