A method for determining potential parental contamination: linkage disequilibrium-based log-likelihood ratio analysis for IVF-PGT

At present, embryologists are attempting to use conventional in vitro fertilization (cIVF) as an alternative to intracytoplasmic sperm injection (ICSI) for preimplantation genetic testing (PGT). However, the potential parental contamination origin of sperm cells and cumulus cells is considered the main limiting factor in the inability of cIVF embryos to undergo PGT. In this study, we established an IVF-PGTA assay for parental contamination tests with a contamination prediction model based on allele frequencies and linkage disequilibrium (LD) to compute the log-likelihood ratio (LLR) under competing ploidy hypotheses, and then verified its sensitivity and accuracy. Finally, comparisons of the effectiveness of SNP-based analysis and LLR-based IVF-PGTA among 40 cIVF embryos was performed, based on both statistical analysis of the parental contamination rate and chromosomal ploidy concordance rate between TE biopsy and ICM isolations. With IVF-PGTA assay, biopsies with 10% maternal contamination could be detected accurately, and contamination caused by sperm cells could be eliminated completely. Utilizing LLR-based or single Nucleotide Polymorphism (SNP) -based analyses, our comprehensive examination of 40 clinically discarded fresh cIVF embryos revealed an absence of paternal contamination. Strikingly, the LLR-based analysis uniquely revealed a mere instance of 24% maternal contamination within the trophectoderm cell (TE) biopsy of 5* embryo. Furthermore, it was solely through this analysis that embryo (9-F) was identified as a triploid of paternal origin. In this study, we developed a new bioinformatics analysis method for identifying parental contamination during IVF-PGT, especially for couples with nonmale factor infertility.