Natural frozen embryo transfer with hCG booster leads to improved cycle outcomes: a retrospective cohort study

PURPOSE: To determine whether luteal support with intramuscular injection of human chorionic gonadotropin 1 day post-LH surge in natural cycle frozen embryo transfer (nFETs) increases ongoing pregnancy rates (OPR). METHODS: Retrospective cohort study of women who underwent natural cycle FET with transfer of a single day-5 or - 6 euploid blastocyst between January 2017 and December 2018 at an academic medical center were divided into two groups based on whether they received hCG 1 day post-LH surge. Patients with uterine factor infertility were excluded. RESULTS: A total of 529 nFET cycles were included. The OPR was significantly higher in the treatment group than in the non-treatment group when controlling for potential confounders such as embryo morphology (69.9% versus 57.4%, p = 0.0119, aOR1.724, 95% CI 1.13-2.65). There were no significant differences observed in the rates of first trimester loss (aOR 1.05, 95% CI 0.032-2.96) or biochemical pregnancy (aOR 0.79, 95% CI 0.31-1.76). Odds ratios were adjusted for patient's age, body mass index, peak endometrial thickness, gravidity, and parity. CONCLUSION: The current data suggest that the hCG booster given to patients within 1 day post-LH surge results in improved cycle outcomes compared to patients who do not receive the booster.