Is there a critical LH level for hCG trigger after the detection of LH surge in modified natural frozen-thawed single blastocyst transfer cycles?

PURPOSE: There is no consensus yet in the literature on an optimal luteinizing hormone (LH) level for human chorionic gonadotrophin (hCG) trigger timing in patients undergoing frozen-thawed embryo transfer (FET) with modified natural cycles (mNC). The objective of our study was to compare the clinical results of hCG trigger at different LH levels in mNC-FET cases. METHODS: This retrospective study was conducted in Istanbul Memorial Hospital ART and Genetics Center. A total of 1076 cases with 1163 mNC-FET cycles were evaluated. LH levels between the start of LH rise (15 IU/L) and LH peak level (> 40 IU/L) were evaluated. Cycles were analyzed in four groups: group A (n = 287) LH level on the day prior to the day of hCG; groups B, C and D, LH levels on the day of hCG: group B (n = 245) LH 15–24.9; group C (n = 253), LH 25–39.9; group D (n = 383) LH ≥ 40. Cycle outcomes in the four groups were compared. RESULTS: Subgroup analyses of mNC-FET groups showed that implantation, clinical and ongoing pregnancy rates, and pregnancy losses were not significantly different in patients with different LH levels on the day of hCG trigger. CONCLUSION: Our study suggests that hCG can be administered at any time between the start of LH rise (≥ 15 IU/L) and LH peak level (≥ 40 IU/L) without a detrimental effect on clinical outcome.