Diploid-aneuploid mosaicism in human embryos cultured to the blastocyst stage.

OBJECTIVE: To examine diploid-aneuploid mosaicism in human in vitro cultured blastocysts. DESIGN: A laboratory study on spare blastocysts from an IVF program. SETTING: University hospital laboratory. PATIENTS(S): Forty-three couples undergoing IVF or intracytoplasmic sperm injection. INTERVENTION(S): Ninety-one blastocysts were spread for fluorescence in situ hybridization using the HCl-Tween 20 method. A total of 6,664 nuclei were analyzed for aneuploidy using fluorescent DNA probes specific to chromosomes 2, 7, and 18. MAIN OUTCOME MEASURE(S): The proportion of aneuploid cells within each blastocyst. RESULTS(S): The incidence of diploid-aneuploid mosaicism among 91 blastocysts examined was 17.6%. All of the mosaic blastocysts were abnormal for only one of the three chromosomes tested, with the incidence of involvement of chromosomes 2, 7, and 18 being 3.3%, 8.8%, and 5.5%, respectively. The majority of the mosaic blastocysts had low proportions of aneuploid cells. Ten of the 16 (62.5%) affected blastocysts were of morphology compatible with implantation. CONCLUSION(S): A considerable proportion of human IVF blastocysts show a form of mosaicism that has been observed in fetal and placental tissues. This mosaicism often arises at the final stage of preimplantation development in vitro and is present in blastocysts of morphology compatible with implantation.