LAUSR

The aim of the study was to determine the accuracy of fetal sex definition by measuring the yolk sac size and the yolk sac–fetal pole distance in the first trimester via ultrasound (US) screening. We enrolled 92 gestational women in this prospective study. In the first trimester of US examination, the gestational sac, the gestational sac–fetal pole distance, and the yolk sac size were measured. When the fetal pole was in the longitudinal position, the distance between the fetal pole and the yolk sac was measured in millimeters (mm). The crown–rump length (CRL) was measured in the same position. US examination at 22 weeks was performed to determine whether the fetal gender was male or female. The genders of the fetuses were recorded. The sexes were also confirmed and recorded after birth. Fifty-five (59.8%) of the newborns were found to be male, while 37 (40.2%) of them were found to be female. We compared the yolk sac size and the yolk sac–fetal pole distance in both the female and male groups. We found that the genders showed a significant difference in terms of yolk sac–fetal pole distance, whereas the yolk sac size showed no significant difference between the genders. The optimal cutoff value of the yolk sac–fetal pole distance was 1.80 mm, with 70% sensitivity and 67% specificity for female gender prediction. The distance also showed an independent association with gender prediction in the first trimester. Yolk sac–fetal pole distance may have the potential to predict gender in the first trimester of pregnancy.