Impact of serum luteinizing hormone level and increment on the day of endometrial transformation on frozen–thawed single blastocyst transfer outcome in the hormone replacement cycle

To analyze the effect of serum luteinizing hormone (LH) level and increment on the day of endometrial transformation on the outcome of frozen-thawed embryo transfer during the hormone replacement cycle. We conducted a retrospective cohort study to analyze the clinical data of 845 women who underwent frozen-thawed embryo transfer during the hormone replacement cycle at Weifang People’s Hospital from January 2019 to December 2021. The women with a median serum LH level 11.97 U/L (0.96 U/L − 24.17 U/L) on the day of endometrial transformation were enrolled. The serum LH levels on the day of endometrial transformation were divided into two groups according to the median. If there was a difference in pregnancy outcome between the high and low LH levels, the range of LH levels was further narrowed. The range of LH between 0 and 25 U/L was divided into one group according to every 5 U/L, and the LH levels of all patients were divided into five groups according to the low to high LH levels. The correlation between the outcome of frozen-thawed embryo transfer and LH level was compared. Women with serum LH > 11.97 U/L on the day of endometrial transformation had higher human chorionic gonadotropin (HCG) positive rates (P = 0.012) and clinical pregnancy rates (P = 0.022) than those with LH ≤ 11.97 U/L. The LH > 15 U/L group had a higher HCG positive rate (OR = 1.274, 95% CI = 1.034–1.699, P = 0.044), while the LH > 20 U/L group had a higher clinical pregnancy rate (OR = 1.879, 95% CI = 1.124–3.287, P = 0.019). Higher serum LH levels and increment on the day of endometrial transformation in the hormone replacement cycle are positively correlated with a higher clinical pregnancy rate in women with normal basal endocrine levels undergoing frozen-thawed embryo transfer. This suggests that elevating the LH levels prior to the transfer of frozen embryos may increase the likelihood of successful embryo implantation and aid in identifying the optimal implantation window. ChiCTR2200060489.