Fetal Genotype-Phenotype Sex Discordance: A Case of 5-Alpha-Reductase Deficiency.

Objective To describe the prenatal and postnatal diagnostic workup leading to the diagnosis of 5-alpha-reductase type 2 deficiency (5AR2D) in a case of 46,XY disorder of sex development (DSD). Case report A first-trimester noninvasive prenatal test (NIPT) on maternal blood revealed a male fetus with a low risk of aneuploidy. However, a female fetus was identified at the second-trimester scan. A repeat sample revealed similar results and ruled out the possibility of both a sample swap or a vanishing twin. At birth, phenotypically female external genitalia were evident, with testes noted in the labioscrotal area. Neonatal blood confirmed a 46,XY complement and a 46,XY DSD genetic panel revealed a 5AR2D. Conclusion Our case and others described in the literature demonstrate that fetal sex discordance detected by a combination of NIPT and subsequent ultrasound examination can be associated with several biological conditions, with DSD being the most significant.