The relationship between embryo quality and the occurrence of multiple pregnancies.

OBJECTIVE: To study the relationship between the quality of the transferred embryos and the occurrence of multiple pregnancies. Embryo quality was defined by the cleavage rate and by morphological parameters such as blastomere size and the presence or absence of anucleate fragments. DESIGN: A retrospective analysis of 1,915 consecutive transfers of fresh embryos between January 1986 and December 1989. SETTING: All the embryo transfers (ETs) were performed in patients from the in vitro fertilization program of the Center for Reproductive Medicine, Vrije Universiteit Brussel, Brussels, Belgium. RESULTS: We confirmed the relationship between the number of embryos transferred and the pregnancy rate (PR): 11.9% of the single, 19.0% of the double, and 34.1% of the triple ETs were successful. Thirty-one percent of these triple embryo replacements resulted in a multiple gestation. At the time of transfer (44 to 48 hours after insemination), we observed that embryos that had undergone at least two mitotic divisions implanted better than two-cell embryos of comparable morphological appearance (implantation rate per transferred embryo: 21.3% versus 12.3%, P less than 0.001) and that heavily fragmented embryos did not implant as well as embryos without or with fewer anucleate fragments (1.5% versus 14.1%, P less than 0.001). The PR, implantation rate, and the incidence of multiple pregnancies increased significantly with the number of good quality embryos that were transferred. CONCLUSIONS: Our study indicated that embryo quality based on morphological observations could predict the occurrence of multiple pregnancies.