Normal newborn with prenatal suspicion of X chromosome monosomy due to confined placental mosaicism.

The recent introduction of cell-free DNA (cfDNA)-based noninvasive prenatal testing (NIPT) offers pregnant women a more accurate method than traditional serum screening methods for detecting fetal aneuploidies. Clinical trials have demonstrated the efficacy of NIPT for Down, Edwards and Patau syndromes. However NIPT approaches that take advantage of single-nucelotide polymorphism (SNP) information potentially allow the identification of triploidy, chromosomal microdeletion syndromes and other unusual genetic variants. To highlight this approach of NIPT we present a rare case of confined placental X chromosome monosomy mosaicism that was prenatally suspected with a single-nucleotide polymorphism-based noninvasive prenatal test. The results of invasive tests (amniocentesis) showed small proportion of X chromosome mosaicism (45, X[5]/46, XX[95]). After birth karyotype of the girl revealed no abnormalities (46 XX), confirming that mosaicism was limited to the placenta. These results highlight the need of patient's informed consent and thorough pretest and postest counseling to ensure that they understand the limitations and advantages of the tests and the implications of the resultss. Sociedad Argentina de Pediatría.