Low Dose hCG Support in Modified Natural Frozen Embryo Transfer Cycles

What is the effect of a single low-dose recombinant hCG injection after embryo transfer (ET) in letrozole-induced modified natural frozen embryo transfer cycles (mNC-FET)?. An observational study was conducted in the university-affiliated referral clinic between 2022 and 2024. Women aged 18-42 with at least one vitrified blastocyst obtained from the previous cycle(s) were included. Ovulation induction for endometrial preparation was initiated with oral letrozol (5 mg/day) for five days. Ovulation was triggered using 6500 IU rec hCG sc when the leading follicle > 17 mm, endometrial thickness > 7.5 mm, and serum progesterone (P) < 1.5 ng/ml. All women received 30 mg dydrogesterone/day po for additional five-day luteal support. On the 6th day, ET was performed. Based on a quasi-randomized design, a group of women additionally received a half single bolus of (3250 IU) rec hCG (sc) on the morning of 3rd day of ET (hCG group). Women who did not receive additional hCG were assigned as controls. One hundred fifty-four women were detected to be eligible for the study among 2150 initiated FET cycles during the period. Demographic data of the groups, including mean women's age, BMI, serum AMH, and infertility etiologies, were comparable in terms of variables. Mean serum progesterone values and the number of transferred embryos were also similar. A significantly higher ongoing pregnancy/started cycle was documented in the hCG group than in controls (46.7% vs 33.6% respectively, p = 0.03*). A single low-dose hCG injection after ET may improve the OPRs of women in letrozole mNC-FET cycles.