LAUSR

The use of polar bodies for preimplantation genetic testing for both single gene defects (PGT-M) and aneuploidy (PGT-A) was pioneered by Verlinsky and colleagues beginning in the late 1980s. For many years, it was applied clinically to diagnose the inheritance of maternal mutations and, using fluorescence in situ hybridisation (FISH) with chromosome specific probes, to detect maternal meiotic segregation errors resulting in aneuploidy. Most clinics now culture to the blastocyst stage and with the advent of vitrification, biopsied blastocysts can be cryopreserved efficiently while the samples are sent to a genetics lab for testing. However, polar body biopsy continues to be used in several European countries with legal or ethical restrictions on the testing of embryos. Although the second polar body can persist to the blastocyst stage, both polar bodies are eventually lost and do not form part of the embryo. Removing both of the polar bodies is therefore minimally invasive. Polar body analysis by NGS-based copy number analysis or SNP genotyping and either karyomapping or meiomapping is highly effective for both aneuploidy and linkage-based testing for maternal mutations. The advantage for PGT-A, in particular, is that only maternal meiotic aneuploidies are identified avoiding the problem of interpreting intermediate copy number changes associated with chromosome mosaicism in multiple cell biopsies. Polar body biopsy therefore remains a valuable alternative strategy for PGT.