The Pregnancy Outcome of Mosaic Embryo Transfer: A Prospective Multicenter Study and Meta-Analysis

Chromosomal mosaicism is at high occurrence in early developmental-stage embryos, but much lower in those at prenatal stage. Recent studies provided evidence on the viability of mosaic embryos by reporting pregnancy outcomes. Expanded research is warranted to evaluate its clinical significance. This is a multi-center prospective cohort study on 137 mosaic, 476 euploid and 835 non-preimplantation genetic testing (non-PGT) embryos from three in vitro fertilization (IVF) providers of three countries in Asia, applying the same preimplantation genetic testing for aneuploidies (PGT-A) reporting criteria. Mosaic embryo transfers (METs) resulted in a significantly lower clinical pregnancy rate (40.1% versus 59.0% versus 48.4%), lower ongoing/live birth rate (27.1% versus 47.0% versus 35.1%) and higher miscarriage rate (33.3% versus 20.5% versus 27.4%) than euploid and non-PGT transfers, respectively. Pregnancy losses after METs were different between embryos carrying numerical and segmental chromosomal abnormalities (p= 0.04). Our meta-analysis concluded that METs gave rise to pregnancies but were associated with a reduced ongoing/live birth rate and a higher miscarriage rate. All 37 MET live births were confirmed viable, among which 8 completed prenatal genetic testing with normal results. Longitudinal investigation on one MET pregnancy evidenced the aneuploidy depletion hypothesis. This is the first multi-center prospective study reporting a full MET pregnancy outcome with complementary information from prenatal genetic testing as compared to euploid and non-PGT cohorts.