Role of intramuscular progesterone supplementation on the day of embryo transfer in artificial frozen cycles

Background Sufficient endometrial preparation with or without progesterone supplementation is crucial in artificial cycles with frozen embryo transfer (FET). We aimed to study the effect of intramuscular progesterone supplementation on the day of embryo transfer (ET) in artificial frozen cycles. Methods A clinical cohort study involved women undergoing FET with artificially prepared endometrium. Serum progesterone levels were assessed on the day of ET. Accordingly, we recruited 177 women with progesterone levels more than 9.2 ng/ml in group 1, and 177 other women with progesterone levels less than 9.2 ng/ml in group 2. Women in group 1 received only 400 mg vaginal progesterone twice-daily after ET, while women in group 2 received additional intramuscular progesterone supplementation. The chemical, clinical, and ongoing pregnancy rates, as well as the pregnancy loss rate, were assessed in both groups. Results Expectantly, both groups showed a significant difference regarding the serum progesterone level on the day of ET (13.43 ± 4.65 vs 4.62 ± 2.77, P = 574). However, with additional intramuscular progesterone supplementation in group 2, both groups showed no significant difference regarding the chemical pregnancy rate (68.93% in group 1 vs 63.84% in group 2, P = 0.311), the clinical pregnancy rate (61.02% in group 1 vs 58.76% in group 2, P = 0.664), ongoing pregnancy rate (56.50% in group 1 vs 53.11% in group 2, P = 0.522), and pregnancy loss rate (7.41% in group 1 vs 9.62% in group 2, P = 0.564). Conclusions Intramuscular progesterone supplementation in women with decreased serum progesterone levels could improve pregnancy outcomes in artificial frozen cycles. Trial registration It was first registered at ClinicalTrials.gov on 8/4/2021 with registration number NCT04837768.