Fetal gender screening by ultrasound at 11 to 13(+6) weeks

To survey the accuracy of fetal gender determination during first trimester screening and scan for congenital anomalies.

A prospective observational study was performed on 496 singleton pregnancies at the first trimester ultrasound screening. The doctor was a certified sonographer of first trimester screening by the Fetal Medicine Foundation(FMF). Ultrasound examination was performed on a GE Voluson 730 Pro, transabdominally, between 11 and 13(+6) weeks. Both transverse and mid-sagittal planes of a section of the fetal genital tubercle were performed to identify the gender. The subsequent gender at birth was obtained from karyotyping reports or hospital birth records.

During the study, 496 patients requested gender information at the time of first trimester screening. Of the patients it was possible to determine gender (441 out of 496), the scan achieved an overall success rate of 91.8% in correctly identifying gender. The success rate for correctly identifying fetal gender (where identification was possible) increased with gestational age, from 71.9% at 11 weeks, 92% at 12 weeks, and 98.3% at 13 weeks, respectively, where gestational age was calculated from the crown-rump length in conjunction with menstrual or ovulation dating (p<0.001). Of the 55 cases where no identification of gender was possible, 39 were in the 11-week gestational age group, representing 40.6% of this category. The overall fetal gender accuracy rate for male fetus was slightly better than female (92.5 versus 91.2%), but was not statistically significant.

This study demonstrated that the gestational age of the fetus has a material effect on the accuracy rate of gender determination. At 12 weeks and over, the average success rate for correctly identifying gender, where gender identification was possible, was 94.8%, with the accuracy at 13 weeks of 98.3% approaching that achieved by invasive testing. Fetal gender identification at 11