Progesterone is a hormone that plays a fundamental role in the reproductive cycle and pregnancy. It is produced by the ovaries following ovulation and works to prepare the uterus for a potential pregnancy. If conception occurs, this hormone continues to support the early stages of gestation, creating and maintaining a suitable environment within the uterus for a developing embryo.
The Role of Progesterone in IVF Success
Progesterone is particularly important in In Vitro Fertilization (IVF) because natural hormonal processes can be altered by fertility treatments. In a typical menstrual cycle, after an egg is released, the remnant follicle transforms into the corpus luteum, which produces progesterone. This hormone signals the uterine lining to thicken and become receptive for an embryo to implant.
During IVF, medications used to stimulate the ovaries and prevent premature ovulation can affect the body’s natural progesterone production. Therefore, external progesterone supplementation is often necessary to ensure the uterine lining remains supportive. This supplementation helps maintain a stable environment, reduce uterine contractions, and support early pregnancy development, increasing the chances of successful implantation and ongoing pregnancy.
Target Progesterone Levels Post-Transfer
After an IVF embryo transfer, maintaining adequate progesterone levels is important for successful implantation and pregnancy. Generally, many clinics aim for progesterone levels above 10-15 ng/mL a few days following egg retrieval to support implantation. Some studies suggest that optimal outcomes for frozen embryo transfers (FETs) are achieved when progesterone levels are sustained between 10 and 20 ng/mL prior to implantation.
However, there is not one universally agreed-upon “perfect” number, and ideal levels can vary slightly among clinics and specific treatment protocols. For instance, some research indicates that a progesterone level of 20.6 ng/mL on the day of embryo transfer may be an optimal cut-off value for predicting ongoing pregnancy rates, particularly in single euploid blastocyst transfers. Conversely, excessively high progesterone levels on the day of the trigger shot in fresh IVF cycles have been associated with lower live birth rates, possibly due to premature endometrial advancement.
While a level below 10.9 ng/mL two weeks after embryo transfer has been linked to a significantly lower live birth rate, some sources indicate that levels below 13.6 ng/mL before FET are associated with poorer clinical and ongoing pregnancy rates. Very low progesterone levels after transfer are generally not considered normal for pregnancy support.
Managing Progesterone Levels
If progesterone levels are insufficient after an IVF transfer, supplementation is commonly used. Progesterone can be administered in several forms, including vaginal suppositories, gels, or tablets, and intramuscular injections. Vaginal administration is often preferred due to its direct delivery to the uterine lining and may be as successful as intramuscular injections for live births.
Intramuscular injections are absorbed slowly and evenly and may help limit spotting or bleeding in early pregnancy. Oral progesterone capsules are generally not recommended for pregnancy support in IVF due to poor absorption. Based on blood test results, a doctor may adjust the dosage or switch the method of administration to optimize levels for the best possible outcome. Very high progesterone levels on the day of the trigger in fresh IVF cycles can be a concern, potentially leading to a less receptive uterine lining, and may prompt a recommendation to freeze embryos for transfer in a later cycle.
Monitoring Progesterone Levels
Blood tests are the standard method for measuring progesterone levels after an IVF transfer. These tests are typically performed a few days after the embryo transfer, often around the time a pregnancy test would be conducted.
For some protocols, progesterone levels may also be checked two days after starting supplementation to confirm adequate levels are being achieved. If pregnancy is confirmed, progesterone supplementation commonly continues throughout the first trimester, usually until about 8 to 10 weeks of gestation, when the placenta takes over hormone production.