This clinical trial is focused on studying infertility and involves the use of two treatments: Estrofem and Cyclogest. Estrofem is a film-coated tablet containing estradiol, a form of estrogen, which is a hormone that plays a key role in the reproductive system. Cyclogest is a pessary, which is a type of medication inserted into the body, containing progesterone, another important hormone for pregnancy. The purpose of this study is to explore the effectiveness of rectally administered progesterone for supporting the luteal phase, which is a part of the menstrual cycle, in hormone replacement therapy frozen embryo transfer (HRT-FET) cycles.

Participants in the study will receive either the rectal form of progesterone or a different form of luteal phase support. The study will monitor the ongoing pregnancy rate at week 12 after the embryo transfer. The trial will also look at other factors such as the levels of progesterone in the blood and urine, any side effects, and the convenience of using the rectal form of Cyclogest. The study aims to determine if the rectal administration of progesterone is as effective as other methods used in HRT-FET cycles.

The trial will continue until the end of 2026, with recruitment starting in November 2023. Participants will be monitored for various outcomes, including the rate of positive pregnancy tests, clinical pregnancies, pregnancy loss, and any complications during pregnancy, such as high blood pressure or preeclampsia. The study will help to understand the best way to support the luteal phase in women undergoing HRT-FET cycles.