The frequency of chromosome anomalies in human preimplantation embryos after in-vitro fertilization.

Previous studies have reported chromosome aberrations in human pre-embryos after in-vitro fertilization (IVF). Although the reason for these abnormalities is not clear, there is evidence that they can arise during gametogenesis, fertilization or cleavage. The present study has examined further the incidence of chromosome abnormalities in human pre-embryos after IVF, using oocytes recovered from normal volunteer women and from women undergoing infertility treatment in an embryo-replacement programme. Chromosome preparations were performed for 75 pre-embryos. Of these 35 (47%) gave at least one metaphase in which analysis was possible. The overall incidence of abnormal pre-embryos was 40% (14/35). The absolute frequency of aberrations was 9% for trisomies, 3% for polyploidies, 26% for structural anomalies and 3% for hypodiploidies. Five pre-embryos were found to be mosaics, three of which had each one trisomic metaphase. In five of the pre-embryos multiple anomalies were found. In 13 of the 14 abnormal pre-embryos the aberrations were found in only one metaphase. The present study demonstrates that trisomic mosaicism may not be a rare event in human pre-embryos. Further evidence is provided that mitotic non-disjunction is important for the production of aberrations in human pre-embryos.