Chromosome analysis of human oocytes recovered from preovulatory follicles in stimulated cycles.

To investigate the incidence and types of abnormalities of chromosome number in oocytes, we recovered preovulatory oocytes from 17 women who were undergoing clomiphene stimulation and laparoscopy because of infertility. Twenty-three oocytes were recovered and studied after they had been fixed with a gradual-fixation method: 17 of the oocytes had numbers of chromosomes in the haploid range (19 to 25 second-metaphase chromosomes), 4 had only 1 to 5 chromosomes, 1 was not analyzable, and 1 had 23 chromosome bivalents in the first metaphase. Of the oocytes with chromosome numbers in the haploid range, nine had an apparently normal haploid set of 23 chromosomes. Two had 1 to 2 additional chromosomes, three lacked 2 to 4 chromosomes, and three had totals of chromosomes that were close to 23 but could not be determined with certainty. We conclude that infertile women undergoing clomiphene stimulation have a high proportion (nearly 50 percent) of oocytes with an abnormal karyotype. If this is also true of fertile women, including those not taking clomiphene, it may explain the high frequency of chromosome aberrations occurring in early spontaneous abortion and the low pregnancy rate after in vitro fertilization.