Association Between Embryo Implantation Rate and Maternal Age in Different Embryo Transplantation Cycles: a Retrospective Cohort Study

The investigators designed a retrospective clinical trial conducted from January 2015 to December 2020 at the Reproductive Medicine Center of the Affiliated Drum Tower Hospital of Nanjing University Medical School. Infertility was defined as the failure of a clinical pregnancy after 12 months or more of regular unprotected intercourse with the same marriage partner. Patients experiencing infertility no younger than the age of 20 who attended the Reproductive Medicine Center of the Affiliated Drum Tower Hospital of Nanjing University Medical School for the first time and had experienced no less than one embryo transplantation between January 2015 and December 2019 were recruited. Patients who had experienced or canceled embryo transplantation cycles for any reason were excluded from this study. The gap year from December 2019 to December 2020 allowed researchers to follow up on the outcomes of pregnancies before 2020. Frozen cycles were performed when high-quality embryos existed to avoid unnecessary ovarian stimulation and oocyte retrieval processes. Investigators were blinded to the outcome of embryo transplantation, and information on pregnancy was gathered through telephone follow-up one year after transplantation.