The association between female age and pregnancy outcomes in patients receiving first elective single embryo transfer cycle: a retrospective cohort study

This study aimed to explore the relationship between female age and pregnancy outcomes in patients undergoing their first elective single embryo transfer (eSET) of in vitro fertilization (IVF) cycles. The retrospective cohort study encompassed 7089 IVF/intracytoplasmic sperm injection (ICSI) patients of the Reproductive Medicine Center, Henan Provincial Peoples' Hospital of China, from September 1, 2016, to May 31, 2022. Patients all received the first eSET in their IVF/ICSI cycles. A generalized additive model (GAM) was employed to examine the the dose-response correlation between age and pregnancy outcomes, namely the clinical pregnancy rate (CPR) and ongoing pregnancy rate (OPR). Logistic regression model was employed to ascertain the correlation between the CPR/OPR and age. The study cohort has an average age of 30.74; 3843 patients got clinical pregnancy rate of 61.40% and ongoing pregnancy rate of 54.21%. The multiple pregnancy rate of is 1.24%. For patients aged 34 and above, the CPR decreased by 10% for every 1-year increase in age (adjusted OR 0.90, 95% CI 0.84-0.96, p < 0.0001). Similarly, the OPR decreased by 16% for every 1-year increase in age (adjusted OR 0.84, 95% CI 0.81-0.88, p < 0.0001). Patients aged 35-37 years had an acceptable OPR of 52.4% after eSET, with a low multiple pregnancy rate (1.1%). Pregnancy outcomes were significantly better in blastocyst cycles compared to cleavage embryo cycles, and this trend was more pronounced in older patients. There was a non-linear relationship between female age and pregnancy outcomes in patients undergoing their first eSET cycles. The clinical pregnancy rate and ongoing pregnancy rate decreased significantly with age, especially in women older than 34 years. For patients under 37 years old, single embryo transfer should be prioritized. For patients over 38 years old with available blastocysts, eSET is also recommended.