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Abstract Study question Does micronized vaginal progesterone (MVP) associated with oral dydrogesterone (DYG) an alternative for luteal support in Letrozole-hcg cycles for thawed embryo transfer? Summary answer The association of MVP and DYG is a non-inferior alternative to only MVP for luteal support in thawed embryo transfer in Letrozole-hcg cycles. What is known already Endometrial preparation is essential for thawed embryo transfer. Several protocols involving different luteal support with progesterones are available. Moreover, the presence of corpus luteum decreases the obstetrical morbidity mainly linked to hypertensive disorders. Letrozole-hcg administration is a good alternative for frozen embryo transfer (FET). However, the literature lacks information about the comparison among the different protocols for luteal support in Letrozole-hcg cycles. Dydrogesterone is an oral progesterone with some unique characteristics which could be utilized with some advantage for luteal support, including oral administration and some immunological activity. Study design, size, duration This is a prospective non-inferiority cohort study performed at an infertility clinic including patients performing the first FET cycle during 2023. Reproductive outcomes were compared between patients receiving 600 mg (3x200 mg) of MPV or 40 mg of DYG plus 400 mg of MVP after Letrozole-hcg administration. Participants/materials, setting, methods All patients (aged 23-39 years) undergoing their first FET cycle during 2023 were included in this study (n = 169), divided into two groups: MVP+DYG (n = 54) or MVP (n = 115) for luteal support after Letrozole-hcg. Letrozole was administered for 5 days (2,5 mg/bid) and hcg was done when a dominant follicle reached 18 mm with a follicular endometrium measuring at least 7 mm. Main results and the role of chance Both groups were equivalent in terms of age, infertility aetiology, BMI and AMH (P 0.05). Moreover, the proportion of cleavage or blastocyst stage was also similar between both groups (57% blastocyst transfer for MVP+DYG and 50% blastocyst transfer for MVP group, P 0.05). The number of transferred embryos was (mean ±SD) 1.6±0.5 for both groups, P 0.05. Furthermore, the number of top-quality embryos (cleavage stage or blastocyst) was also similar, P 0.05. Moreover, clinical pregnancy ( 12 weeks) was 42% in MVP+DYG group versus 31% in the MVP group (-0.22-1.27, P = 0.156) and the early pregnancy loss per positive hcg test did not differ (18% for MVP+DGY and 22% for MVP, P = 0.687). In addition, we performed a multivariable analysis controlling possible confounders for clinical pregnancy: BMI, age, AMH, embryo quality, infertility aetiology and embryo stage during the transfer, and only age (0.86; 95%CI -0.229 to -0.064, P = 0.001) was related to clinical pregnancy. Limitations, reasons for caution The main limitation is the cohort design of our study, with an inherent risk of bias (selection bias). Moreover, we calculated this study to achieve the power for a non-inferiority comparison, not superiority comparison. Wider implications of the findings This is the first study comparing MVP+DYG to only MVP in patients submitted to FET using the Letrozole-hcg protocol. We demonstrated in this non-inferiority study the usefulness of adding DYG. Moreover, our results were promising showing a trend towards better pregnancy rates after MVP+DYG. Trial registration number not applicable
filho et al. (Mon,) studied this question.