Ultrasound measurement learning of fetal sex during the first trimester: does the experience matter?

Abstract

Objective: To determine the probability of correctly diagnosing fetal sex during the first trimester by ultrasound according to crown-rump length (CRL) and previous ultrasound experience. Methods: A cohort study was performed from March 2012 to April 2013. The 2,314 first trimester pregnancy ultrasounds were examined. Eight sonographers, according to previous ultrasound experience, were divided into two groups: senior and junior. 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. Results: In 1,986 cases, fetal sex was diagnosed, with a success rate of 90.1%. A directly proportional relationship between the rate of success in fetal sex diagnosis and CRL (P,0.001) was described. The rate of success in male fetuses was significantly higher than in female fetuses (94.6% vs 86.3%, respectively), P,0.001. In the senior sonographers group, the rate of overall success was 89.2% vs 90.5% in the junior group, the difference not being significant. The experience of sonographers did not reach statistical significance (95% confidence interval: 0.871-1.031; P=0.213). Conclusion: The prediction of fetal sex over 65 mm of CRL in both sexes is approximately 95% and from 76 mm onward is 99%. Both CRL and fetal sex influence the rate of success; however, the experience of a sonographer has not proven to be an influential factor. These results could be explained because the technique for diagnosing sex during the first trimester is very simple to learn.