Sonographic determination of fetal gender before 25 weeks gestation

Sonographic determination of fetal gender was attempted prospectively in 121 consecutive routine obstetric scans between 10 and 25 weeks gestation. There were two sets of twins in this group, so a total of 123 fetuses was studied. Birth records were subsequently available in 113 of these fetuses at which time conclusive data regarding the fetal gender could be analyzed. Of these 113 fetuses, a sonographic determination of fetal gender was made in 53 (47%). There were three errors in this group of 53 (error rate 6%) and all of these incorrect determinations were male fetuses thought to be females in utero by sonography. There were no errors in those called male by sonography in utero. The male-female mix demonstrated a higher number of males in the group in whom sonographic determination was possible. There was a lower number of males than females in the group in whom the gender of the fetus could not be detected by sonography. A significantly higher number of males (60) than females (53) was present in the study population for no apparent reason.