Progesterone and estrogen in the context of frozen embryo transfer: standards, importance, and effectiveness of IVF programs

Duration of Progesterone Intake After a Frozen Embryo Transfer (FET)

The transfer of frozen embryos (FET) as part of a IVF program requires comprehensive and prolonged hormonal support. Progesterone plays a key role here, as it ensures the stability of the luteal phase and creates optimal conditions for implantation. Generally, its use continues until 11-12 weeks of pregnancy, that is, until the placenta fully takes over hormonal functions. This process, called luteo-placental transition, is a critical step for pregnancy maintenance.

Some specialists emphasize that gradually reducing medication doses as the body transitions to natural hormone production reduces fluctuations and supports the preservation of the implanted embryo. The gynecologist adjusts the dosage individually, based on the protocol and the dynamics of hormonal analyses. Depending on the patient's characteristics, different forms of administration are used: vaginal, intramuscular, subcutaneous. Combined schemes have shown high effectiveness in large-scale clinical studies, particularly among women with multiple IVF failures.

Monitoring Progesterone and Estrogen Levels: Practical Aspects

Before the transfer of the frozen embryo, monitoring progesterone levels is a mandatory condition. It determines the chances of a successful implantation and healthy pregnancy.

• The minimum progesterone level (threshold) should be ≥ 8.8-10 ng/ml on the day of embryo transfer in scheduled FET cycles.
• If the level is below 8.8-12 ng/ml, additional treatment (subcutaneous or intramuscular progesterone) is prescribed. This helps increase live birth rates among women with initially low hormonal levels.
• The optimal range for progesterone is between 12 and 20 ng/ml. However, excessively high levels (> 40 ng/ml) may decrease implantation chances because they alter endometrial receptivity and reduce the “implantation window.” Scientific publications also indicate that an excess of progesterone can modify the expression of endometrial receptors.

Estrogen serves as a marker of endometrial receptivity to progesterone. Despite the absence of strict target values, in practice, levels >180-200 pg/ml with an endometrial thickness of at least 7-8 mm and preserved trilaminar structure are sought. Monitoring the dynamics is important: a gradual increase in estrogen indicates normal endometrial preparation and creates conditions for successful embryo development and synchronization.

On our blog, we have previously discussed important topics: “Estrogens: their role in the female body and their influence on reproductive health” and “Progesterone During Pregnancy: Role, Levels, and Impact on the Body.” These articles help deepen understanding of hormonal regulation in reproductive medicine.

Hormonal Support After Embryo Transfer

After embryo transfer, progesterone support remains essential. In women who continue pregnancy, hormone levels are generally higher during the first 12 weeks following transfer. This underscores the need for constant monitoring and prompt adjustment of treatment. Some protocols extend support up to 14 weeks, especially in patients with complicated medical histories.

Recent studies confirm that stable progesterone levels at the beginning of pregnancy significantly increase the chances of live birth. In turn, a judicious combination of progesterone and estrogen creates optimal conditions for successful implantation and embryo development. It is important to note that the balance between these hormones influences not only pregnancy occurrence but also reduces the risk of pregnancy loss.

Personalized Approach in IVF Programs

Today, reproductive medicine clinics implement individualized protocols based on the patient's age, medical history, endometrial morphological characteristics, hormone levels, and genetic factors. This personalized approach increases the chances of pregnancy success and smooth progression. The development of new technologies, including genetic screening of embryos and real-time hormone monitoring, enhances the efficiency of IVF and FET programs.

Useful Links to Studies

1. Endometrial preparation for frozen embryo transfer: update on clinical practices — PMC
2. Serum progesterone level on the day of embryo transfer in frozen embryo transfer cycles — the truth lies in the details — PMC
3. Impact of endometrial preparation on early pregnancy losses and live birth rates after frozen embryo transfer: a large multicenter cohort study (14,421 frozen cycles) — PMC
4. Progesterone and estrogen levels are associated with live birth rates after frozen embryo transfers in artificial cycles — PMC
5. Systemic progesterone optimizes outcomes of scheduled frozen embryo transfers: the only level I evidence consistently supports intramuscular administration — Fertility and Sterility