To describe reproductive outcomes in patients managed with a single-dose IM rescue protocol versus those not requiring rescue and explore the association of very low pre-ET progesterone with lower live birth rates or higher miscarriage rates.
Key Findings:
LBR was significantly lower in the Rescue group with pre-ET P4 <5 ng/mL (19.2%) compared to those with P4 5–7.49 ng/mL (43.8%) and 7.5–9.99 ng/mL (39.0%).
Miscarriage rates were higher in the <5 ng/mL group (46.7%) compared to the ≥5 ng/mL group (9.9%).
Rescue with P4 ≥5 ng/mL showed LBR similar to No-Rescue (41.8% vs. 39.2%).
Among borderline cycles (P4 9.1–9.9 ng/mL), LBR was numerically higher with rescue (57.1%) than without (40.0%), but underpowered.
ROC AUC was 0.609 with a Youden cutoff of 5.3 ng/mL.
Interpretation:
Pre-ET P4 <5 ng/mL was associated with poor per-transfer prognosis, but this finding is assay-specific and not a validated deferral rule.
Limitations:
No cycles were deferred, limiting the ability to isolate the rescue effect.
The study is exploratory and specific to the Cobas e411 ECLIA assay, requiring recalibration for other platforms.
The small sample size of the borderline cycles limits statistical power.
Conclusion:
The findings indicate that low pre-ET P4 levels are associated with poor outcomes, but further validation is necessary.
