The chromosome constitution of human preimplantation embryos fertilized in vitro

The chromosome constitution of five haploid, 178 diploid and11 triploid embryos fertilized in vitro was determined afterfixation on day 2 or day 3 of development. Karyotype analysisof 178 diploid embryos revealed abnormalities in 40 (22.5%)cases: 34 (19.1%) aneuploids, four (2.2%) mosaic embryos andtwo (1.1%) structural anomalies were identified. The majorityof aneuploid karyotypes (28/34) involved a single chromosomebut six embryos had aneuploidy of two or three chromosomes.The E group was most frequently involved in aneuploid karyotypes(10/23 hyperdiploid embryos) and trisomy 16, the most commonsingle anomaly in diploid embryos, was detected in 2.2% (4/178)of cases. Only one case of sex chromosome monosomy was identified.An excess of female karyotypes was detected in abnormal cases(sex ratio 0.48); this ratio was significantly (p< 0.05)different from that observed in normal cases (74: 64, XY: XX).The incidence of aneuploidy increased with maternal age butthis did not reach statistical significance. Embryo morphologyand growth rate, assessed by embryo development rating (EDR),did not distinguish between normal (mean score 7.9; mean EDR96.1) and aneuploid (mean score 8.1; mean EDR, 92.1) embryos.Numbers of hyperploid (n = 17) and hypoploid (n= 11) embryos(non-mosaic cases involving single chromosomes) were not statisticallydifferent. The relative proportions of chromosomes involvedin trisomic karyotypes showed a remarkable similarity to thepattern in spontaneous abortions. Pronuclear status was an unreliablepredictor of ploidy. Small numbers of karyotyped triploid embryosrevealed equal proportions of XXX, XXY and XYY embryos