Received December 20, 2022
Accepted June 23, 2023

PURPOSE: Does the use of 400 mg pessaries of micronized progesterone provide comparable results as pessaries of 200 mg x2, in terms of progesterone levels in hormonal replacement cycles for embryo transfer? METHODS: Retrospective cohort study based on 299 embryo transfer treatments under artificial endometrial preparation carried out at Instituto Bernabeu. 131 patients received 1 pessary of 400 mg b.i.d. (group A) and 168 received 2 pessaries of 200 mg b.i.d. (group B). RESULTS: Mean serum progesterone levels were similar between groups (A:13,64 ng/mL ± 4,47 vs B:13,88 ng/mL ± 7,17). There were no differences in suboptimal progesterone levels between groups (A:11,5% vs B:16,8%). In terms of patients receiving additional progesterone supplementation, there were no differences between groups (A:26% vs B:35,3%.). No differences between groups were observed in clinical outcomes: pregnancy rate (PR) (A:55% vs. B:54,8%), biochemical pregnancy loss rate (BPLR) (A:13,4% vs. B:17.6%), miscarriage rate (MR) (A:17,9% vs. B:19,8%) and ongoing pregnancy rate (OPR) (A:36,5% vs. B:34,1%). CONCLUSIONS: One pessary of 400 mg of natural micronized progesterone twice daily appears to be non-inferior to the use of two-200 mg of vaginal capsules twice daily in terms of progesterone levels in HRT cycles and might reduce the frequency of suboptimal progesterone levels on the day of embryo transfer.