Chromosomal integrity of human preimplantation embryos at different days post fertilization

Abstract

Introduction: In order to investigate the dynamics of genomic alterations that occur at different developmental stages in vitro, we examined the chromosome content of human preimplantation embryos by molecular-cytogenetic techniques at the single-cell level, up to 13 days post fertilization.

Methods: The embryos were genetically analyzed several times during their development in culture; each embryo was first analyzed by FISH at 'Day 3' post fertilization, than during its growth in vitro and the third analysis was performed at development arrest, then the entire blastocyst was analyzed by comparative genomic hybridization (CGH/aCGH).

Results: We found that while on 'Day 3' only 31% of the embryos were detected as normal, on 'Day 5-6', 44% of the embryos were classified as normal and on 'Day 7', 57% were normal. On 'Days 8-13', 52% of the embryos were classified as chromosomally normal. One third of the embryos that were chromosomally abnormal on 'Day 3', were found to be normal at development arrest point.

Discussion: These dynamic changes that occur at early developmental stages suggest that testing a single blastomere at 'Day 3' post fertilization for PGD might inaccurately reflect the embryo ploidy and increase the risk of false aneuploidy diagnosis. Alternatively, blastocyst stage diagnosis may be more appropriate.

Fig. 1

Flow diagram summarizing the experimental design. Each embryo was first analyzed by FISH at ‘Day 3’ post fertilization, again through its growth in vitro (not all embryos were sampled at all time points) and last analysis was performed at developmental arrest. Numbers in brackets represent embryos with complete results

Fig. 2

Summary of the survival of embryos in culture (by days)

Fig. 3

Example of array-CGH result from a ‘Day 6’ embryo [sample number 90, Table 3, t (10;18)]. In addition to the unbalanced translocation, the microarray analysis also shows a single copy loss of the entire chromosomes 16 and 22

Fig. 4

The relative contribution of each chromosome in the aberrant embryos

Fig. 5

Embryos classified as abnormal at development arrest: percentage of embryos harboring one, two, three and four or more aberrations

Fig. 6

The percent of euploid embryos at different days of development. (Asterisks) Based on one cell diagnosis