Comparable implantation rates with fresh vs frozen embryo transfer suggests that controlled ovarian hyperstimulation has an adverse effect on conception outcome

A retrospective comparison of fresh vs frozen embryo pregnancy rates. All frozen embryos transferred used in the analysis including deselected embryos from the oocyte retrieval cycle, and twice-frozen embryos. Pregnancy and implantation rates following fresh or frozen embryo transfers were similar. The similar outcomes despite the obvious disadvantages for the frozen-thawed embryo suggests that some other factor reduces the chance of embryo implantation on oocyte-retrieval cycles. An adverse affect of controlled ovarian hyperstimulation on the uterine environment is a strong possibility.