CYTOGENETIC ANALYSIS OF HUMAN OOCYTES AND EMBRYOS IN AN INVITRO FERTILIZATION PROGRAM

Oocytes (unfertilized and preovulatory) and embryos (normal and polypronuclear), which were donated to research by patients undergoing procedures of assisted reproductive treatment, were analysed for cytogenetic abnormalities. A total of 362 oocytes and embryos were analysed. The unfertilized oocytes with readable metaphases (53.4%) gave 25.2% chromosomal abnormality with diploidy being the main aberration observed. A high incidence of premature chromosome condensation (PCC) was observed and the incidence of PCC in oocytes exposed to colcemid was significantly higher (14/62, 22.6%) than in those not exposed to this treatment (3/41, 7.3%, P < 0.05). When chromosomal anomalies and PCC in the unfertilized oocytes were correlated to various patient criteria such as stimulation regimen, number of human menopausal gonadotrophin ampoules, peak oestradiol levels, age of patient and number of previous attempts, none of the criteria tested had any significant relationship to the incidence of chromosomal abnormality. However a significant increase in the incidence of PCC was noted in the gonadotrophin-releasing hormone (GnRH) 'flare' group (6/15, 40.0%) compared to the GnRH 'down-regulation' group (11/88, 12.5%). The incidence of chromosomal abnormalities among preovulatory oocytes was 16.7% and diploidy was the only abnormality noted. For embryos arising from two-pronuclear oocytes, the chromosomal constitution related mainly to embryo quality. The rate of chromosomal abnormality for apparently good quality embryos was 23.5% and for poor or fragmented embryos 83.3%. The majority (77.3%) of the readable metaphase plates for polypronuclear 1-cell and cleaved embryos showed grossly abnormal chromosome complements but 19% of the cleaved embryos contained sets of normal diploid chromosomes. The chromosomal abnormalities observed among oocytes and embryos are discussed in relation to similar material analysed by other in-vitro fertilization (IVF) programmes. The relevance with respect to assessing IVF techniques, patient factors and improvement of culture conditions is considered.