Determinación del sexo genérico fetal por ultrasonografía precoz: 11-14 semanas / Determination of fetal gender sex by early ultrasound: 11-14 weeks

RESUMO

Objective. To assess the accuracy (positive predictive value) of fetal sex determination at 11-14 weeks of gestation by routine ultrasound. Methods. Fetal gender assessment by ultrasound was prospectively carried out in 267 fetuses at 11-13+6 weeks of gestation (45-84 mm crown-rump length) in an unselected population including twin and singleton pregnancies. Transabdominal scan was performed by a single operator who examined the genital region in a midsagittal plane of the fetus as described by Efrat et al. in 1999. The fetal gender was assigned as male if the angle of the genital tubercle to a horizontal line trough the lumbosacral skin surface was greater than 30º and female when the genital tubercle was parallel or convergent (less than 30º) to the horizontal line. Sex confirmation data was obtained postnatally from hospital registries, parents information or by ultrasound performed after 22 weeks of gestation. Results. Fetal gender assessment was successfully achieved in 97 percent (259/267). The accuracy of sex determination (positive predictive value) increases from 74,2 percent at 11 weeks, trough 90,5 percent at 12 weeks to 95,7 percent at 13 weeks. Male fetuses were incorrectly assigned as female in 29,2 percent of cases at 11 weeks, 12,2 percent at 12 weeks and 5 percent at 13 weeks. In contrast, 14,3 percent of the female fetuses at 11 weeks were incorrectly assigned as male and this false-positive rate was 4,5 percent and 3,3 percent at 12 and 13 weeks, respectively. Conclusion. The clinical value of early ultrasound determination of fetal sex includes confirmation of zygosity and analysis of chorionic villous sampling in twin pregnancies, early information for demanding parents and a powerfull method to decide whether to carry out prenatal invasive testing in pregnancies at risk of sex-linked genetic disorders, because it would be unnecessary in pregnancies with female fetuses. Our results suggest that early sex determination by routine ultrasound reaches the best accuracy at the 13th week of gestation.