The chromosome constitution of human preimplantation embryos fertilized in vitro

Abstract

The chromosome constitution of five haploid, 178 diploid and 11 triploid embryos fertilized in vitro was determined after fixation on day 2 or day 3 of development. Karyotype analysis of 178 diploid embryos revealed abnormalities in 40 (22.5%) cases: 34 (19.1%) aneuploids, four (2.2%) mosaic embryos and two (1.1%) structural anomalies were identified. The majority of aneuploid karyotypes (28/34) involved a single chromosome but 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 common single 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 but this did not reach statistical significance. Embryo morphology and growth rate, assessed by embryo development rating (EDR), did not distinguish between normal (mean score 7.9; mean EDR 96.1) 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 statistically different. The relative proportions of chromosomes involved in trisomic karyotypes showed a remarkable similarity to the pattern in spontaneous abortions. Pronuclear status was an unreliable predictor of ploidy. Small numbers of karyotyped triploid embryos revealed equal proportions of XXX, XXY and XYY embryos.

Confirmation of diagnosis in preimplantation genetic diagnosis (PGD) through blastocyst culture: preliminary experience

“…Mosaicism persists to the blastocyst stage as it has been described in early stage embryos (Munné et al, 1994b;Munné and Cohen, 1998;Harper et al, 1995;Jamieson et al, 1994). In our series 7/8 blastocysts are mosaics.…”

Chromosomal differences in susceptibility to meiotic aneuploidy

“…Oocytes ( Recently, Jamieson et al [1994] studied 178 diploid embryos fertilized in vitro and found 43 (24%) to be nonmosaic aneuploid. About half were hyperploid and half hypoploid, supporting the idea that trisomic and monosomic conceptions occur equally frequently but that monosomics are lost before implantation.…”

A retrospective study of preimplantation embryos diagnosed with monosomy by fluorescence in situ hybridization (FISH)

“…Studies of human embryos using FISH have shown that approximately 70% of preimplantation embryos have a mosaic aneuploidy karyotype (Harrison et al, 2000;Voullaire et al, 2000;Wells and Delhanty, 2000;Sandalinas et al, 2001;Bielanska et al, 2002). Mosaicism has also been observed by other methods such as performing karyotyping on day 2 or 3 embryos (Jamieson et al, 1994). Comparative genomic hybridization (CGH) on metaphase chromosomes offers the advantage of allowing all chromosomes to be analyzed.…”