The “Imperfect” Embryo: A Clinical Case of Successful Pregnancy after Transfer of a Mosaic Embryo

Abstract

Introduction. Chromosomal mosaicism is a common finding detected by preimplantation genetic testing for aneuploidy (PGT-A). For a long time, mosaic embryos were excluded from transfer; however, current professional society guidelines allow their use in the absence of euploid embryos. Objective to based on the analysis of a clinical case, to discuss current approaches to patient counseling when chromosomal mosaicism is detected, criteria for embryo selection for transfer, and the need for prenatal diagnosis. Materials and Methods. Retrospective analysis of a single clinical case (case report). Results. The patient was a 29‑year‑old woman with tubal infertility and a history of adverse obstetric events (missed miscarriage, ectopic pregnancy, tubectomy). Her partner was 41 years old, normozoospermic, and had healthy children from a previous relationship. The first in vitro fertilization (IVF) cycle yielded 14 oocytes, 10 were fertilized, and 4 reached the blastocyst stage. PGT‑A revealed: T1 — mosaic monosomy 12 (40%); T2 — aneuploid; T3 — mosaic trisomy 21 (40 %); T4 — aneuploid. Embryo T1 (morphology 4BA) was transferred, resulting in an intrauterine pregnancy. The patient declined invasive prenatal diagnosis, citing normal ultrasound findings and normal prenatal screening results. At 39–40 weeks of gestation, delivery was performed by caesarean section; a male infant weighing 3800 g, length 50 cm, Apgar score 8/9 was born. The child is healthy, with no signs of chromosomal abnormalities. Conclusion. Transfer of a low‑level МЕ (monosomy 12) can lead to the birth of a healthy child. The decision should be individualized, taking into account clinical, genetic, and psychological aspects.