Faster embryo growth rate in vitro increases probability of pregnancy in assisted reproduction cycles

Introduction: Human preimplantation embryos are characterized by highly variable morphology and developmental potential. We examined factors that may contribute to embryo implantation and pregnancy, including in vitro embryo cleavage or growth rate. Methods: This study involved 494 assisted reproduction treatment cycles. For each embryo, the number of blastomeres and morphological grade were identified on days 1, 2, and 3 after oocyte retrieval. The rate of cleavage of each embryo was represented by the slope of the regression equation involving the number of blastomeres and the days of incubation. These characteristics were compared between pregnancy and non-pregnancy cycles. Logistic regression analysis was used to determine which variables contribute to pregnancy. Results: The embryo cleavage rate was significantly faster in pregnancy than in non-pregnancy cycles. Logistic regression analysis showed that four factors play a significant role in embryo implantation and pregnancy: total number of embryos available, female age, and total cleavage rate and average grade of transferred embryos. Stratification by female age revealed that cleavage rate is most important in women aged 40 years and older. Conclusions: Embryos with a faster cleavage rate are more likely to result in pregnancy than slower growing embryos, especially in older women.