Determinación del sexo fetal en el primer trimestre de la gestación: Estudio prospectivo

Abstract

Objective: To assess the accuracy of fetal gender determination by ultrasound at 11-14 weeks of gestation in a large cohort of unselected population. Methods: A prospective cross-sectional study was performed in 636 consecutive pregnancies at 11-14 weeks of gestation, attending for first trimester ultrasound screening. The genital region was examined in the mid-sagittal plane to detect the sagittal sign and the direction in which the genital tubercle pointed (cranial for males, caudal for females) both as markers of fetal gender. The clinical confirmation of fetal gender was obtained from telephonic interviews after delivery or from karyotype in cases scheduled to amniocentesis for conventional indications. Results: Fetal gender was correctly determined by ultrasound in 86.3% of the fetuses. The accuracy of sex assignment was higher in male fetuses than in female fetuses (90.6% of the males fetuses vs 83.1% of the females were correctly assigned, p<0.05) and increased with gestational age from 72% at 11-11+6 week's to 92% at 12-12+6 week's, and 95% at 13-13+6 week's gestation (p<0.01). Conclusion: Prenatal gender assignment by ultrasound has a high accuracy rate at 13 to 13+6 weeks. These results suggest that invasive testing can probably be performed in fetuses identified as males at this gestational age. However in fetuses identified as females, the decision regarding invasive testing should be postponed until a higher gestational age is achieved.