Chromosomal, gestational, and neonatal outcomes of embryos classified as a mosaic by preimplantation genetic testing for aneuploidy.

OBJECTIVE: To understand the clinical risks associated with the transfer of embryos classified as a mosaic using preimplantation genetic testing for aneuploidy. DESIGN: Analysis of data collected between 2017 and 2023. SETTING: Multicenter. PATIENTS: Patients of infertility treatment. INTERVENTION: Comparison of pregnancies resulting from embryos classified as euploid or mosaic using the 20%-80% interval in chromosomal intermediate copy numbers to define a mosaic result. MAIN OUTCOME MEASURES: Rates of spontaneous abortion, birth weight, length of gestation, incidence of birth defects, and chromosomal status during gestation. RESULTS: Implanted euploid embryos had a significantly lower risk of spontaneous abortion compared with mosaic embryos (8.9% [n = 8,672; 95% confidence interval {CI95} 8.3, 9.5] vs. 22.2% [n = 914; CI95 19.6, 25.0]). Embryos with mosaicism affecting whole chromosomes (not segmental) had the highest risk of spontaneous abortion (27.6% [n = 395; CI95 23.2, 32.3]). Infants born from euploid, mosaic, and whole chromosome mosaic embryos had average birth weights and lengths of gestation that were not statistically different (3,118 g and 267 days [n = 488; CI95 3,067, 3,169, and 266, 268], 3052 g and 265 days [n = 488; CI95 2,993, 3,112, and 264,267], 3,159 g and 268 days [n = 194; CI95 3,070, 3,249, and 266,270], respectively). Out of 488 infants from mosaic embryo transfers (ETs), one had overt gross abnormalities as defined by the Centers for Disease Control and Prevention. Most prenatal tests performed on pregnancies from mosaic ETs had normal results, and only three pregnancies produced prenatal test results reflecting the mosaicism detected at the embryonic stage (3 out of 250, 1.2%; CI95 0.25, 3.5). CONCLUSION: Although embryos classified as mosaic experience higher rates of miscarriage than euploid embryos (with a particularly high frequency shortly after implantation), infants born of mosaic ETs are similar to infants of euploid ETs. Prenatal testing indicates that mosaicism resolves during most pregnancies, although this process is not perfectly efficient. In a small percentage of cases, the mosaicism persists through gestation. These findings can serve as risk-benefit considerations for mosaic ETs in the fertility clinic.

Two clinical case reports of embryonic mosaicism identified with PGT-A persisting during pregnancy as true fetal mosaicism.

The health risks associated with transferring embryos classified as mosaic by preimplantation genetic testing for aneuploidies (PGT-A) are currently unknown. Such embryos produce PGT-A results indicating the presence of both euploid and aneuploid cells and have historically been deselected from transfer and grouped with uniformly aneuploid embryos as 'abnormal'. In recent years, numerous groups have reported the intentional transfer of mosaic embryos in the absence of uniformly euploid embryos, largely observing births of seemingly healthy babies. However, it remains to be understood whether the embryonic mosaicism invariably becomes resolved during the ensuing pregnancy, or whether the placenta and/or fetal tissues retain aneuploid cells, and if so to what potential clinical effect. Here, we report two cases of mosaicism persisting from the embryonic stage to the established pregnancy. Case 1 involved an embryonic low-level segmental mosaic loss in Chromosome (Chr) 1, which was confirmed in amniocentesis as well as in brain tissue of the products of conception. This pregnancy was terminated due to the chromosomal pathologies associated with 1p36 deletion syndrome, such as severe intellectual disability. Case 2 involved a low-level mosaic Chr 21 trisomy, which was confirmed with chorionic villus sampling and amniocentesis. The ensuing pregnancy was terminated after ultrasound identification of severe abnormalities in the placenta and fetus. Together, these two cases should be taken into account for risk-benefit assessments of prospective mosaic embryo transfers.

Neonatal and clinical outcomes after transfer of a mosaic embryo identified by preimplantation genetic testing for aneuploidies.

RESEARCH QUESTION: Do clinical and neonatal outcomes differ between mosaic embryo transfers (MET) and euploid embryo transfers (EET)? DESIGN: This retrospective cohort study compared the implantation rate, live birth rate (LBR) and miscarriage rate between 513 euploid embryos and 118 mosaic embryos (72 whole chromosome mosaic [WCM], 40 segmental mosaic and six complex mosaic). Blastocysts were analysed using preimplantation genetic testing for aneuploidies with next-generation sequencing, followed by a single vitrified-warmed embryo transfer. Trophectoderm biopsies were classified as mosaic if they had 20-80% abnormal cells. RESULTS: Overall, EET resulted in a significantly higher implantation rate (47.0%) and LBR (40.7%) than MET (implantation rate 39.0%, P = 0.005; LBR 28.8%, P = 0.008) and WCM embryos (implantation rate 37.5%, P = 0.01; LBR 22.2%, P = 0.007) after covariate adjustment. Segmental mosaic embryos had an implantation rate (47.5%) and LBR (45.0%) comparable to those of euploid embryos. Mosaic embryos with a high percentage of aneuploid cells (≥60%) showed a significantly lower LBR (10.5% versus 40.7%, P = 0.03) than euploid embryos after covariate adjustment, with three of the five implantations of mosaic embryos resulting in miscarriage. Neonatal outcomes did not differ significantly between the mosaic and euploid groups. Of the 34 women with a live birth after MET, 13 had a prenatal or postnatal genetic testing result, and no abnormalities were found. CONCLUSIONS: Mosaic embryos were associated with a lower LBR, while segmental mosaic embryos had similar clinical outcomes to euploid embryos. Mosaic embryos with a high aneuploidy percentage (≥60%) should be assigned a low transfer priority. Neonatal outcomes did not differ significantly between the euploid and mosaic groups.

The live birth in a woman with resistant ovary syndrome after in vitro oocyte maturation and preimplantation genetic testing for aneuploidy.

We report the pregnancy and live birth achieved after in vitro maturation (IVM) of oocytes and PGT-A in a 23-year-old patient suffering from ovarian gonadotropin resistance. A woman with resistant ovary syndrome (ROS) had secondary amenorrhea, high FSH levels (25.34 mIU/mL) and LH (29.6 mIU/mL), low estradiol levels (15.2 pg/mL), and high serum AMH levels (38.0 ng/mL), associated with an increased antral follicle count (AFC) of 45. Without gonadotropin priming and HCG trigger, ultrasound-guided transvaginal oocyte retrieval was performed. Aspiration of antral-stage follicles allowed the retrieval of 15 immature oocytes. After oocyte collection, immature oocytes were cultured in the IVM medium. Following IVM, six of them reached metaphase II stage. Resultant matured oocytes were fertilized by intracytoplasmic sperm injection (ICSI). Embryos obtained were cultured to the blastocyst stage. On day 5, three embryos reached blastocyst stage. Trophectoderm biopsy and PGT-A were performed on two better quality embryos on day 5 after fertilization. Two biopsied embryos were reported to be euploid. PGT-A was performed utilizing next-generation sequencing (NGS\MPS). One embryo was transferred in an artificial thaw cycle and resulted in a viable intrauterine pregnancy and live birth. Our experience indicates that there is no requirement for gonadotropin stimulation and use of b-hCG trigger prior to IVM in patients with ROS. The results suggest that oocytes obtained with IVM in patients with ROS are capable of meiotic and mitotic division, fertilization, and generation of euploid embryos. IVM appears to be a valuable approach in patients with ROS, allowing them to have genetically connected offspring.