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ABSTRACT We present a unique case in which non-invasive and invasive prenatal diagnoses showed abnormal, but discordant, results. A patient with abnormal non-invasive prenatal test ( NIPT) results, indicating a 99% risk for monosomy X, was referred to our center for genetic counseling and confirmatory studies. Cytogenetic analysis of uncultured mesenchymal core of chorionic villi ( CV) revealed a mosaic male karyotype consisting of two abnormal cell lines: one with monosomy X and the other with an isodicentric chromosome Y. Array analysis of the trophoblast confirmed the NIPT results. Based on the CV results, the patient opted for termination of pregnancy. After extensive counseling by a clinical geneticist about the possible outcomes and by a gynecologist about the risk of a second-trimester abortion procedure, the patient agreed to undergo early amniocentesis. Amniocentesis confirmed that the fetus had a male karyotype with an isodicentric chromosome Y, and the single nucleotide polymorphism ( SNP) array profile suggested absence of the monosomy X cell line. The male infant was expected to be infertile. The patient finally decided to continue the pregnancy. Our case confirms that NIPT results are comparable with those of short-term cultured CV investigating the cytotrophoblast. Our patient was not aware that the NIPT results reveal the placental karyotype, which sometimes may be different from the fetal karyotype. Pretest counseling and providing the risk figures for false-positive and false-negative NIPT results are of great importance in order to discourage women from terminating pregnancies based on NIPT results alone. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]