# Urine Progesterone Level as a Diagnostics Tool to Evaluate the Need for Luteal Phase Rescue in Hormone Replacement Therapy Frozen Embryo Transfer Cycles

## TL;DR

Urine progesterone levels can help determine if additional progesterone is needed during frozen embryo transfers to improve pregnancy outcomes.

## Contribution

This study introduces urine progesterone as a novel diagnostic tool for assessing luteal phase support in HRT-FET cycles.

## Key findings

- Urine progesterone levels significantly differ based on serum progesterone thresholds.
- A urine progesterone cut-off of ≥4000 ng/mL is associated with higher live birth rates.
- Patients with higher urine progesterone had an 1.8 times higher odds of live birth.

## Abstract

Additional progesterone administration during the luteal phase enhances reproductive outcomes in Hormone Replacement Therapy Frozen Embryo Transfer (HRT-FET) cycles in patients with low serum progesterone (P4). In this study we wanted to explore the use of urine P4 as a diagnostic tool during the luteal phase. This prospective observational cohort included a total of 464 HRT-FET cycles. The protocol entailed oral oestradiol (6 mg/24 h), followed by vaginal micronised progesterone (400 mg/12 h). On the day of blastocyst transfer, urine and serum samples were collected. Urine samples were analysed using an ARCHITECT automated immunoassay. A significant difference was found in median urine P4 between patients with serum P4 higher or lower than 11 ng/mL: 6400 ng/mL IQR [2528; 11,930] vs. 3408 ng/mL IQR [592; 6688], p < 0.001. The optimal cut-off to achieve live birth was a urine P4 ≥ 4000 ng/mL. The live birth rate was significantly higher in patients with urine P4 ≥ 4000 ng/mL, 48% (107/222) vs. 35% (45/130), respectively (p = 0.013). The odds ratio for live birth was 1.8 in patients with urine P4 ≥ 4000 ng/mL, 95% CI [1.067; 3.018], p = 0.028. The findings of the present study suggest that urine progesterone could be a valuable diagnostic tool to evaluate the need for additional progesterone in HRT-FET cycles.