P-437 Are serum progesterone levels predictive for reproductive outcomes in artificial cycles if individualized luteal phase support is only administered when progesterone is below 5 ng/ml?

Abstract Study question Do serum progesterone levels predict reproductive outcomes in artificial cycles when individualized luteal phase support is administered only if progesterone falls below 5 ng/ml? Summary answer The low 5 ng/ml progesterone threshold appears to be sufficient for the patient not to require additional progesterone injections when progesterone is above 5 ng/ml. What is known already Serum progesterone (P4) level is negatively associated with ongoing pregnancy rate (OPR) and miscarriage rate in artificially prepared frozen embryo transfer (FET) cycles using standard micronized vaginal progesterone (MVP) for luteal phase support. Individualized luteal support is considered a successful rescue strategy in cycles with low serum progesterone levels eliminating the effect of P4 levels on outcome. Cut-off levels for this rescue strategy range from 8.8 to 10 ng/ml. Study design, size, duration A retrospective single-centre cohort study including a total of 1,016 vitrified-warmed single blastocyst transfers performed at a tertiary fertility centre between October 2021 and December 2022. Blastocysts of ≥ 3CC Gardner score were eligible for vitrification on day 5 or day 6 (Vit-kit or Vit-kit NX, FuijiFilm). Embryos were warmed and subsequently transferred on the same day which was day 5 in the cycle, regardless if the embryo was vitrified on day 5 or day 6. Participants/materials, setting, methods We included 595 patients undergoing an artificially prepared embryo transfer (ET) cycle using MVP 800mg BID for luteal phase support. Serum P4 levels were determined on the day of ET with the initiation of additional injections of subcutaneous P4 from the day after ET in patients with P4 < 5ng/ml. Primary endpoint was OPR. Multivariable logistic regression was performed to correct for confounders. Generalized estimating equations (GEE) models were fitted for primary and secondary outcomes. Main results and the role of chance OPR was comparable for the 3 groups: 9/40 (22.5%) for patients with P4 <5ng/ml, 64/275 (23.3%) for patients with P4 5-10 ng/ml and 181/701 (25.8%) for patients with P4 >10ng/ml (p = 0.377). No significant association between P4 category and likelihood for OPR was found after adjusting for confounders. Early clinical miscarriage rate was significantly different between the 3 groups: 5/40 (12.5%) in patients with P4 <5ng/ml, 26/275 (9.5%) with P4 5-10ng/ml and 37/701 (5.3%) with P4 >10ng/ml (P = 0.005). Limitations, reasons for caution Higher clinical miscarriage rate in cycles with a P4 level under 10 ng/ml questions the efficacy of rescue progesterone in cycles with a low P4. The patient population also exists of a subgroup of PGT-a tested cycles which was not included as a potential confounder in this analysis. Wider implications of the findings The 5 ng/ml P4 threshold appears to be sufficient for the patient not to require additional P4 injections when P4 is above 5 ng/ml. Consequently, a significantly lower proportion of cycles would need to be supplemented with rescue progesterone; 3.8% versus 31.3% for the 10 ng/mL cut off. Trial registration number ONZ-2023-0223