Progesterone is a hormone with diverse applications in reproductive health. It plays a key role in the female reproductive system, influencing processes from the menstrual cycle to pregnancy maintenance. Understanding its functions provides context for its medical uses and why pregnancy can occur while taking it.
Progesterone’s Role in the Body
Progesterone is a steroid hormone primarily produced in the ovaries after ovulation. Smaller amounts are also made by the adrenal glands and, during pregnancy, by the placenta. Its main function in females is to prepare the uterus for a potential pregnancy each month.
During the menstrual cycle, progesterone helps thicken the uterine lining, known as the endometrium, making it suitable for a fertilized egg to implant. If pregnancy occurs, levels rise to maintain the uterine lining, support the developing embryo, and prevent uterine contractions that could lead to miscarriage. Beyond reproduction, progesterone also influences bone density and neurological processes.
Progesterone for Birth Control
Progesterone, or its synthetic forms called progestins, is widely used in various contraceptive methods to prevent pregnancy. These include the progestin-only pill (mini-pill), injections, implants, and hormonal intrauterine devices (IUDs). Progestin-only contraception primarily works by thickening cervical mucus, hindering sperm movement.
It also suppresses ovulation in many cycles, preventing egg release. Additionally, it can thin the uterine lining, making it less receptive to implantation. While highly effective, with perfect use often exceeding 99% effectiveness, no birth control method is 100% foolproof. Typical use rates are slightly lower, accounting for factors like missed doses, meaning a small chance of pregnancy remains.
Progesterone for Fertility and Pregnancy
In contrast to its contraceptive use, progesterone is also prescribed to support fertility and maintain pregnancy. For individuals undergoing fertility treatments, such as in vitro fertilization (IVF), progesterone supplementation is important to prepare the uterine lining for embryo implantation. IVF procedures can sometimes affect the body’s natural progesterone production, requiring external supplementation.
Progesterone is also used to help prevent miscarriage, especially in women with a history of recurrent miscarriages or early pregnancy bleeding. It helps maintain the uterine lining and supports the developing pregnancy by preventing uterine contractions and modulating the immune response. Treatment typically continues through the first trimester or until the placenta takes over enough progesterone production, usually around 8 to 10 weeks.
Other Factors Affecting Pregnancy Risk
Several variables can influence the risk of pregnancy while taking progesterone. For contraceptive uses, inconsistent or missed doses significantly reduce effectiveness. For example, the progestin-only pill must be taken at the same time every day for protection.
Certain medications can interact with progesterone, reducing its absorption or effectiveness. These may include some antibiotics, anticonvulsants, and herbal supplements like St. John’s wort. Malabsorption issues due to gastrointestinal conditions could also impact how much progesterone the body receives. Additionally, a person might already be pregnant when they begin progesterone therapy, which the medication would not prevent.
What to Do If You Suspect Pregnancy
If you are taking progesterone and suspect you might be pregnant, a home pregnancy test is a good first step. These tests detect human chorionic gonadotropin (hCG), a hormone produced during pregnancy. Following a positive home test, contact a healthcare provider for confirmation.
A doctor can perform blood tests or an ultrasound to confirm the pregnancy and assess its viability. Do not discontinue progesterone medication without consulting a healthcare professional, as abrupt cessation could have adverse effects depending on why it was prescribed. Your healthcare provider will guide your next steps.