Minimizing mosaicism: assessing the impact of fertilization method on rate of mosaicism after next-generation sequencing (NGS) preimplantation genetic testing for aneuploidy (PGT-A).

PURPOSE

Advances in preimplantation genetic testing (PGT) have led to practice changes in assisted reproductive technologies (ART), enabling fertility centers to transfer single embryos while maintaining excellent ongoing pregnancy rates, reducing miscarriage rates, and dramatically reducing ART-associated multiple pregnancies. The introduction of next-generation sequencing (NGS) allows PGT laboratories to assess for embryo mosaicism-although the true incidence and reproductive potential of predicted mosaic embryos are controversial. Due to concern for genetic contamination from other spermatozoa, most reference laboratories require use of intracytoplasmic sperm injection (ICSI) for single gene preimplantation genetic diagnosis (PGT-M). However, in PGT for aneuploidy (PGT-A), conventional insemination (IVF) is typically permissible. The purpose of this study was to evaluate rates of euploid, aneuploid, and mosaic in trophectoderm biopsy samples from embryos in IVF versus ICSI PGT-A cycles. Secondary aims were to assess sex ratio, and subtypes of aneuploidy and mosaicism in IVF versus ICSI PGT-A cycles.

METHODS

We performed a retrospective review of women undergoing PGT-A at a single academic fertility center from July 1, 2015, to September 1, 2017. In all cycles, PGT-A was performed via trophectoderm biopsy on day 5 or 6 and analyzed using NGS at a single reference lab. We collected and compared patient demographics, fertility testing, cycle characteristics, and PGT-A outcomes between IVF and ICSI cycles.

RESULTS

Three hundred two PGT-A cycles were included for analysis: 75 IVF and 227 ICSI cycles, resulting in 251 IVF and 724 ICSI biopsied blastocysts. Mean oocyte age of included cycles was 38.6 years (IVF) and 38.5 years (ICSI), p = 0.85. Baseline characteristics of IVF and ICSI PGT-A cycles were similar with the exception of semen parameters: IVF cycles had higher sperm concentration and total motility compared to ICSI cycles. PGT-A outcomes did not differ between IVF and ICSI cycles: euploid 27.9% (IVF) versus 30% (ICSI); aneuploid 45.4% (IVF) versus 43.1% (ICSI); no result 4.4% (IVF) versus 6.2% (ICSI). Though not significant, we identified a trend toward higher rate of mosaicism in IVF (25.9%) versus ICSI (20.9%). Among mosaic embryos, a lower percentage of simple mosaic embryos resulted from IVF (53.8%) versus ICSI (70.2%). Among aneuploid embryos, a non-significant higher percentage of complex aneuploidy resulted from IVF (16.3%) versus ICSI (9%). IVF resulted in a non-significant higher proportion of cycles with no transferrable embryos (42.7%) versus ICSI (36.6%). Numerical and sex chromosome involvement in mosaicism and aneuploidy were similar between IVF and ICSI cycles.

CONCLUSION

IVF and ICSI NGS PGT-A have similar rates of euploid, aneuploid, and no result embryos, though IVF may result in higher rates of mosaicism and demonstrates differences in proportions of mosaic and aneuploid subtypes compared to ICSI. ICSI may be preferable to conventional insemination to minimize the rate of mosaic results in NGS PGT-A cycles.