Non-invasive prenatal testing for fetal sex determination: is ultrasound still relevant?

Early prenatal diagnosis of fetal sex is necessary to optimize pregnancy management in families known to be at risk of some heritable disorders. The demonstration of cell-free fetal DNA (cffDNA) in the mother's blood has made it possible to identify Y chromosome sequences in maternal blood and to determine fetal sex noninvasively, during the first trimester. This procedure can significantly reduce the number of invasive procedures for women with fetuses at risk of sex-linked diseases and optimize the management of these pregnancies. Fetal sex can be diagnosed by ultrasound with the same sensitivity and specificity, but later in pregnancy. We performed a review of the published literature evaluating the use of cffDNA and ultrasound for prenatal determination of fetal sex during the first trimester of pregnancy. We present the feasibility of the two methods and their impact on clinical practice. We applied a sensitive search of multiple bibliographic databases including Pubmed (MEDLINE), EMBASE, the Cochrane Library and Web of science between 1998 and 2013. Sixteen reports of the determination of fetal sex in maternal blood and 13 reports of the determination by ultrasound met our inclusion criteria. We found a sensitivity and specificity of nearly 100% from 8 weeks of gestation for cffDNA and from 13 weeks of gestation for ultrasound respectively. Based on this review, we conclude that fetal sex can be determined with a high level of accuracy by analyzing cffDNA and at an earlier gestation than ultrasound. Ten years after the first feasibility study, the French National Authority for Health (HAS) released a technological assessment report on the determination of fetal sex in maternal blood, which has resulted in validating this test for reimbursement by the national health insurance fund for the following indications: X-linked recessive disease and congenital adrenal hyperplasia.