Chromosome investigations in early life. I. Human oocytes recovered in an IVF programme.

Fifty-five oocytes recovered in an in-vitro fertilization (IVF) programme and remaining unfertilized when observed 42 h after insemination were prepared for chromosomal analysis. Sixteen oocytes displayed no polar body at the time of fixation and were supposed to be in metaphase I. In fact only two of them were in diakinesis, the others containing a diploid set of metaphase II chromosomes indicating that in 89% of the cases oocytes achieved meiosis without any extrusion of the first polar body. Thirty-nine oocytes in metaphase II were analysed. Nine were abnormal showing three D nullosomies, one G disomy, one double disomy for a 3 and a D chromosome, one deletion of the long arm of a G chromosome, one cell with extra chromosomes and/or chromosome breaks, one endoreduplication and one tetraploidy. The overall rate of abnormalities reached 22%. This high rate of chromosome anomalies can be explained by the nature of this population of fertilization failure, the frequently advanced maternal age and the use of superovulation treatments.