The effect of endometriosis on implantation: Results from the Yale University in vitro fertilization and embryo transfer program

Objective: To investigate the effect of endometriosis on implantation. Design: Case-control study from Yale University IVF-ET program. Patients: Two hundred eighty-four consecutive IVF cycles were analyzed retrospectively. Patients with endometriosis only (n = 35; 89 cycles) were compared with an age-matched control group with tubal infertility (n = 70; 147 cycles) and also to a group with unexplained infertility (n = 15; 48 cycles). Data from the endometriosis group was analyzed further in subgroups of minimal-mild (43 cycles) and moderate-severe (46 cycles). Results: No difference was found in the number and the quality of oocytes retrieved and fertilization rates between the endometriosis, the tubal infertility, and the unexplained infertility groups. The quality and the number of embryos transferred in each group were comparable. A trend toward reduced pregnancy rate per transfer (14.8%) in the endometriosis versus tubal or unexplained infertility groups (25.7% and 23.3%, respectively) was observed. Implantation rate (gestational sac per transferred embryo) was significantly lower in the endometriosis versus the tubal infertility group (3.9% versus 8.1%; unexplained infertility group, 7.2%). Analysis of first cycles only across all groups revealed that the implantation rate also was significantly lower in the endometriosis versus the tubal infertility group (3.1% versus 9%; unexplained infertility group, 6.7%). Within the endometriosis group, although the pregnancy rate per cycle and per transfer were similar in subgroups, patients with minimal-mild endometriosis had the lowest implantation rate. Conclusion: We conclude that, in patients with endometriosis, implantation rate is low. Abnormal implantation, which may be secondary to endometrial dysfunction or embryotoxic environment, is a factor in endometriosis-associated subfertility.