Progesterone is a naturally occurring hormone that plays a significant role in the female reproductive system. It helps regulate the menstrual cycle and prepares the uterus for a potential pregnancy. Produced primarily by the ovaries, and later by the placenta during pregnancy, progesterone contributes to creating a suitable environment for a fertilized egg to implant and develop. Synthetic versions of this hormone, known as progestins, are widely used in various medical applications.
How Progesterone Prevents Pregnancy
Synthetic progesterone, or progestin, functions as a contraceptive through several mechanisms. It thickens cervical mucus, creating a barrier that makes it difficult for sperm to travel through the cervix and reach an egg, reducing fertilization likelihood.
Progestins also alter the uterine lining, or endometrium, making it thinner and less receptive to a fertilized egg, which prevents successful implantation. High doses of progestin can also suppress ovulation, preventing the release of an egg from the ovary.
Common forms of progestin-only contraception include mini-pills, injections, implants, and hormonal intrauterine devices (IUDs). While some progestin-only methods also suppress ovulation, this is not their primary contraceptive action, especially for lower-dose formulations.
Why Pregnancy Can Still Occur
Despite the effectiveness of progesterone-based contraception, pregnancy can still occur due to several factors, often related to how the method is used. Contraceptive effectiveness is categorized into “perfect use” (consistent and correct use) and “typical use” (real-world conditions). For progestin-only pills, for example, perfect use can be up to 99% effective, but typical use drops to about 91%.
Missed doses are a common reason for reduced efficacy, particularly with progestin-only pills, which require strict adherence to a daily schedule. Missing a dose by even a few hours can decrease their effectiveness, as progestin levels need to remain consistent.
Interactions with other medications can also compromise the effectiveness of progesterone contraception. Certain medications and herbal supplements can accelerate the metabolism of progestins, leading to lower hormone levels in the body. This can diminish the contraceptive’s ability to prevent pregnancy.
Illnesses involving severe vomiting or diarrhea can reduce the absorption of oral contraceptives, making them less effective. If the pills are not fully absorbed into the bloodstream, their contraceptive action may be impaired. Additionally, while rare, contraceptive method failures can occur, such as the expulsion of an IUD, which happens in approximately 3% to 11% of users.
Progesterone’s Role in Supporting Pregnancy
Beyond its use in preventing pregnancy, progesterone plays an important role in supporting and maintaining a healthy pregnancy. After ovulation, progesterone prepares the uterine lining to receive a fertilized egg by thickening it and increasing blood vessel development, creating a nutrient-rich environment for implantation. If pregnancy occurs, the corpus luteum continues to produce progesterone, and eventually, the placenta takes over this production, ensuring sustained support for the growing fetus.
In fertility treatments, such as in vitro fertilization (IVF) cycles, progesterone is often medically supplemented to aid in establishing and sustaining pregnancy. This is particularly important because the medications used in some fertility procedures can suppress the body’s natural progesterone production. Supplementation helps maintain the uterine lining and supports the early embryo’s development, promoting successful implantation and reducing uterine contractions that could interfere with pregnancy.
Progesterone is also utilized in specific cases to help prevent recurrent miscarriages. For women with a history of miscarriage who experience bleeding in early pregnancy, vaginal progesterone supplementation has shown to increase live birth rates. This hormone helps prevent contractions and modulates the maternal immune response to tolerate the developing embryo.
What to Do if You Suspect Pregnancy
If you are using progesterone-based contraception and suspect you might be pregnant, recognizing early signs is important. Common early indicators can include a missed period, breast tenderness, nausea, fatigue, and increased urination. However, these symptoms are not exclusive to pregnancy and can be caused by other factors.
The first step is to take a home pregnancy test, which detects human chorionic gonadotropin (hCG), a hormone produced during pregnancy. When used correctly, these tests are accurate, especially if taken after a missed period. If the home test is positive, or if you have symptoms but the test is negative, consult a healthcare provider for confirmation and guidance.
It is important not to discontinue any prescribed progesterone medication without consulting your healthcare provider. Progesterone can be prescribed for various conditions, including supporting an existing pregnancy, and abruptly stopping it could have unintended consequences. Your provider can confirm pregnancy, assess your situation, and advise on appropriate next steps.