The addition of dydrogesterone improves the outcomes of pregnant women with low progesterone levels when receiving vaginal progesterone alone as luteal support in HRT‐FET cycles

PURPOSE: Vaginal progesterone (VP) alone has been used as luteal support (LS) in HRT‐FET cycles without measuring serum progesterone concentrations (SPC) because it can achieve adequate intrauterine progesterone levels. However, several reports showed that the co‐administration of progestin produced better outcomes than VP alone. We tried to address this discrepancy, focusing on SPC. METHODS: VP was given to 180 women undergoing HRT‐FET. We measured SPC when pregnancy was diagnosed on day 14 of LS. We compared assisted reproductive technology outcomes between VP alone versus VP + dydrogesterone (D). RESULTS: When using VP alone, average SPC in the miscarriage cases (9.6 ng/mL) were significantly lower compared with the ongoing pregnancy (OP) cases (14.7 ng/mL). The cut‐off value for progesterone, 10.7 ng/mL, was a good predictor for the subsequent course of the pregnancy. Of 76 women receiving D ± VP from the start of LS and achieving a pregnancy, the numbers of OP were 44 (84.6%) in SPC ≥ 10.7 ng/mL and 20 (83.3%) in SPC ≤ 10.7 ng/mL with no significant difference. CONCLUSION: VP alone resulted in lower SPC in some pregnant women in HRT‐FET cycles and exhibited a lower OP rate. The co‐administration of D improved an OP rate of low progesterone cases to the level comparable with non‐low progesterone cases.