Abstract
BACKGROUND: The relevance of oestrogen (E(2)) levels on human chorionic gonadotropin (hCG) trigger day and clinical pregnancy outcomes was unclear. This study aimed to investigate whether E(2) levels on the hCG trigger day affect pregnancy outcome in long-acting gonadotropin releasing hormone agonist (GnRHa) down-regulated in-vitro fertilization/intracytoplasmic sperm injection-embryo transfer (IVF/ICSI-ET) cycles. METHODS: This is a retrospective study including 6967 patients undergoing their first long-acting GnRHa down-regulated IVF/ICSI-ET cycles at the Reproductive Medicine Centre of Nanjing Drum Tower Hospital from January 2016 to December 2021. Smooth curve fit analyses were conducted to identify the relationship between serum E(2) levels and the clinical pregnancy rate (CPR), along with the live birth rate (LBR). Threshold effect analyses were conducted to figure out potential cut-off values. Further investigation was also carried out for different types of embryos. RESULTS: Both CPR and LBR declined as the serum E(2) levels on the hCG day elevated. CPR reduced significantly when the serum E(2) levels exceeded 5000 pg/mL. While considering the influence of different types of transferred embryos, the blastocyst transfer was more vulnerable to the elevation of serum E(2) levels than cleavage-stage embryos, and CPR of blastocyst transfer decreased obviously when serum E(2) levels were equal to or greater than 5000 pg/mL. Meanwhile, a higher E(2) level leads to a higher incidence of moderate or severe ovarian hyperstimulation syndrome (OHSS). CONCLUSION: The CPR decreased significantly as E(2) levels increased with serum E level higher than 5000 pg/mL on the hCG day, which was more obvious in blastocyst transfer than cleavage-stage embryo transfer. In addition, the incidence of moderate-to-severe OHSS also significantly increased. Therefore, the whole embryo freezing might be a better choice in patients undergoing long-acting GnRHa down-regulated IVF/ICSI cycles with higher serum E(2) level on the hCG trigger day instead of embryo transfer.