Sonographic fetal sex determination in the first trimester: study in 2314 pregnancies and literature review

To evaluate the success rate and reliability of fetal sex determination in first trimester between 11-13+ 6 weeks and make a comparative study with other studies. A cohort study was performed. 2314 first trimester pregnancy ultrasounds were examined. For fetal sex estimation, the method of a sagittal section and the relation between the angle formed by the genital tubercle and spinal column was used. Diagnosis of fetal sex was issued in 1986 cases with 90.1% success rate. In 328 cases (14.2%) no gender assignment was achieved. A directly proportional relationship between success rate in fetal sex diagnosis and crown-rump length (CRL) (p < 0.001) was described; with CRL over 65 mm, the prediction of fetal sex is above 95% and from 77 mm is close to 100%. With CRL < 51 mm, the success rate is less than 80% in both sexes. The simplest and best performing technique is the relation between the angle formed by the genital tubercle and spinal column. Success rate below 60 mm is less than 90% overall, so it would have to be wary of establishing the fetal sex, especially if it involves a decision as to avoid an invasive test.