P-595 What to expect from “standard vaginal progesterone regimen” in Hormone Replacement Therapy Frozen Embryo Transfer (HRT-FET) – do different products result in different serum levels?
Authors: Humaidan P , Jensen M B , Reich M C , Alsbjerg B 
Published: June 2023

Abstract

Study question
Do luteal serum progesterone levels (P4) vary in relation to time of blood sampling, the type and dosing of vaginal progesterone products used for HRT-FET?

Summary answer
Significant differences in luteal serum P4 levels exist between time of blood sampling as well as between different vaginal progesterone products and the administration regimen.

What is known already
Mid-luteal P4 levels below 9-11 ng/ml have been shown to negatively affect reproductive outcomes in HRT-FET cycles. Formulations of vaginal progesterone products differ as progesterone can be suspended in vegetable hard fat, in a vegetable lipophile liquor, be prepared in an oil-in-water emulsion carrier, or mixed in a tablet. Moreover, dosing regimens vary from one to three times daily, and BMI, age, and parity affect serum P4 levels; importantly, no consensus exists in terms of optimal time point to measure P4 in relation to administration, the specific serum P4 cut-off level to use or the most optimal vaginal progesterone product.

Study design, size, duration
Cohort study including 488 HRT-FET blastocyst transfers performed from January 2020 to November 2022 in patients undergoing a “standard vaginal progesterone regimen”. Each patient participated only once in the study. To compare the vaginal progesterone product used in the present study, we reviewed the most recent literature, including data from six studies, using three different products in six different regimens; all studies were cohort studies, including between 227 -1150 patients undergoing a “standard” HRT-FET protocol.

Participants/materials, setting, methods
A total of 488 patients in a public Fertility Clinic underwent HRT-FET, including endometrial preparation with oral oestradiol (6mg/24hours), followed by vaginal micronized progesterone, 400mg/12hours (Cyclogest®). Blood sampling on the blastocyst transfer day was standardised to two to four hours after progesterone administration. In contrast, P4 was measured randomly on the day of pregnancy testing.
For comparison a review of the literature from six HRT-FET cohort studies using either Crinone®, Utrogestan® or “PIVET”-pessaries was performed.

Main results and the role of chance
The mean serum P4 (2-4 hours after administration) on the day of blastocyst transfer in our cohort was 15.4 ±6.6ng/ml. On the day of pregnancy testing (random time points) serum P4 levels were divided into four groups, depending on the time from progesterone administration to blood sampling: &lt;2hours, &gt;2&lt;4hours &gt;4&lt;6hours and &gt;6hours.The mean P4 levels were 14.7 ±6.3ng/ml, 15.6 ±5.8ng/ml, 14.3 ±4.9ng/ml and 12.9 ±6.4, respectively, and a significant difference was seen, between P4 levels measured 2-4 hours and &gt;6 hours after vaginal administration (p = 0.03).
As regards the product, the mean P4 levels in this study (Cyclogest®) was significantly different from the reviewed P4 levels of other “standard” HRT-FET cohorts, using three different products (Uterogestan®, Crinone® and the “PIVET-pessary”) 12.1 ±7.0ng/ml (p &lt; 0.001), 7.6 ±3.2ng/ml (p &lt; 0.001) and 29.3 ±20.3ng/ml (p &lt; 0.001), respectively.
As regards the dose, a significant difference in P4 levels was seen between dosing regimens in two cohorts when using the same product (Crinone®) 90mg x 3 vs. 90 mg x 2; 11.3 ±4.7ng/ml and 7.6 ±3.2ng/ml, respectively, p &lt; 0.001.
Interestingly, when comparing another product (Utrogestan®) used in different dosing regimens, 400mg x 2 vs. 200mg x 3, no difference in P4 levels was seen, 12.1 ±7.0ng/ml and 11.3 ±5.1ng/ml, P = 0.09.

Limitations, reasons for caution
In HRT-FET serum P4 levels reflect the exogenous administration, only, and P4 fluctuations depend on the route and number of administrations, as well as absorption and metabolization. The reviewed data used for this comparison between different progesterone products and regimens derive from cohorts with different characteristics and blood sampling timings.

Wider implications of the findings
Luteal serum P4 measurement is important, however, standardization of blood sampling in relation to the latest vaginal progesterone administration is mandatory to obtain correct levels. Clinicians should be aware of the significant differences in P4 levels related to dose and vaginal absorption between different types of vaginal progesterone products.

Trial registration number
EudraCT no.: 2019-001539-29