Determination of fetal gender by first trimester ultrasonography

Abstract

Objective: To assess the accuracy of first trimester ultrasonography in determining fetal sex by orientation of genital tubercle in relation to spine in a midsagittal plane.Material and methods: Between May 2000 and 2001, 110 patients were studied from 11 to 14 weeks of gestation (average 12.1 weeks) at first trimester ultrasonography. The genital region was examined in a midsagittal plane and the fetal gender was assigned as male if the angle of the genital tubercle to a horizontal line through the lumbosacral skin surface was greater than 30° and female when the genital tubercle was parallel or convergent (<30°). All final results were checked after birth.Results: Among 148 patients, only in 16 (10.8%) fetal sex was not determined. In 132 patients (89.2%), genital tubercle was identified and sex was determined. There were 106 (80.3%) hits and 26 mistakes (19.7%).Conclusion: The diagnosis of fetal sex at first trimester has an important role in case of X‐linked anomalies so invasive procedures can be avoided if fetuses are female. Our results are similar to others in literature. The accuracy of gender determination by ultrasonography was 80.3%. Most common mistake was to assign male fetuses as female. We believe that this error is due to the angle variation of the genital tubercle during the exam.