Embryonic mosaicism as a cause of errors and discordant results of prenatal diagnosis of chromosomal diseases

Specialists working in the field of prenatal diagnosis of chromosomal diseases regularly face the problem of mosaicism. The existence of placenta-limited mosaicism is well known, in which the fetus has a normal chromosomal set, and certain chromosmic abnormalities can be found in the placenta. There is, however, another type - embryonic mosaicism. In this case, a normal chromosomal set can be found in the cells of the placenta, while the fetus has a chromosomal pathology. A variant of mosaicism is also possible, in which different variants of the abnormal karyotype are present in the placenta and in the fetus. This paper examines several clinical cases of embryonic mosaicism identified during prenatal diagnosis of chromosomal abnormalities, discusses possible causes of such results and ways to optimize diagnostic algorithms. The study included five patients who underwent invasive prenatal diagnostics and/or NIPT at the Institute of Obstetrics and Gynecology named after D. Ott in 2012-2023. Diagnosis of chromosomal pathology was performed using standard karyotyping, FISH, CMA, and NIPT. Possible reasons for discordant results and ways to optimize diagnostic algorithms are discussed.

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