RESUMEN
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.