Fetal Sex Results of Noninvasive Prenatal Testing and Differences With Ultrasonography

To assess the causes of reported discordance between noninvasive prenatal testing (NIPT) and ultrasound or other clinical information. METHODS: In this retrospective, observational study, all cases in which single-nucleotide polymorphism (SNP)–based NIPT reported normal sex chromosomes and the laboratory was notified by the patient or health care provider of discordance between NIPT and observed or expected fetal sex from clinical information were reviewed. When discordances were unresolved after internal and external laboratory clerical data review or repeat ultrasound imaging, additional clinical records, genetic testing results and pregnancy outcomes were reviewed. RESULTS: Of the 1,301,117 eligible NIPT cases, fetal sex discordances were reported in 91 (0.007%; 1:14,300; 95% CI 1:11,600–1:17,800); partial or complete outcome information was available for 83 of 91 cases. In 30 of 83 (36%) cases, karyotyping was performed, and sufficient clinical information was provided to establish the diagnosis of disorders of sexual development. The disorders of sexual development were classified into three categories: 46,XY disorders of sexual development (n=19), 46,XX disorders of sexual development (n=4), and sex chromosome disorders of sexual development (n=7). In 28 of 83 (34%) cases, the cause of the apparent discrepancy was attributable to human error, predominantly phlebotomy labeling or ultrasound misassignment. In 25 of 83 cases, a diagnosis was not possible; the outcome reported was either abnormal (18/83, 22%) or no abnormalities were reported (7/83, 8%). When normal sex chromosomes were predicted by SNP-based NIPT and clinical information was discordant, disorders of sexual development were common. Internal laboratory clerical data review and re-imaging confirmed the NIPT fetal sex reports in 34% cases, providing reassurance that no further evaluation was necessary. CONCLUSION: Identification of apparent fetal sex discordances with NIPT results, and reporting this suspicion to the laboratory, provides an opportunity for further evaluation to identify the cause of apparent discordances and the involvement of a multi-disciplinary team, as necessary to prepare for postnatal care. We propose a protocol for evaluation of these cases. FUNDING SOURCE: This study was funded by Natera, Inc.