THE USE OF FIRST POLAR BODIES FOR PREIMPLANTATION DIAGNOSIS OF ANEUPLOIDY

A large proportion of patients undergoing in-vitro fertilization (IVF) are aged greater than or equal to 35 years. It has been estimated tha t in this age group, 50% of embryos are chromosomally abnormal, with a neuploidy being the major contributing factor. Since the origin of mos t aneuploidies is maternal meiosis I non-disjunction, unfertilized ooc ytes could be safely screened for aneuploidy by analysing their first polar bodies. To determine the feasibility of first polar body aneuplo idy analysis, polar bodies were analysed by fluorescence in-situ hybri dization (FISH) using probes simultaneously for chromosomes X, Y, 18, 13/21 or X, Y, 18 and 16. Within 6 h of retrieval, 88% showed a normal segregation involving a single chromosome of each kind, with double-d otted hybridization signals, corresponding to dyads (chromosomes in me taphase I composed of two chromatids). The rest showed non-disjunction of full dyads (6%), or an unbalanced pre-division of dyads (6%), whic h gives a segregation of one chromatid or one dyad and a chromatid wit h the first polar body. But only 34% of polar bodies analysed 24 h aft er retrieval or later showed a normal segregation, with most of the ot her polar bodies showing balanced pre-division, with two separated hyb ridization signals for all the chromosomes analysed. The rates of non- disjunction and unbalanced pre-division after greater than or equal to 24 h in culture were similar to the rates in fresh oocytes. When both types of aneuploidy were considered together, an increase of aneuploi dy with maternal age was detected, which although slight, was signific ant (P = 0.025). Because dyads seem to undergo rapid pre-division shor tly after polar body retrieval, performance of FISH aneuploidy analysi s of polar bodies is therefore only recommended when conducted within 6 h of their retrieval.