When taken correctly, birth control pills generally prevent ovulation. This article will explain how these pills work to prevent pregnancy and discusses factors that can affect their effectiveness, including situations where ovulation might still occur.
The Mechanism of Birth Control Pills
Combination birth control pills contain synthetic versions of the hormones estrogen and progestin. These hormones work together to prevent pregnancy through several actions, primarily by suppressing the signals that trigger ovulation.
The synthetic hormones in the pill reduce the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland. FSH is necessary for egg development, and the LH surge triggers the release of a mature egg. By keeping FSH and LH levels consistently low, the pills prevent an egg from maturing and being released.
In addition to stopping ovulation, combination pills create other conditions that make pregnancy unlikely. They thicken the cervical mucus, making it harder for sperm to travel through the cervix and reach an egg. The hormones also thin the lining of the uterus (endometrium), which makes it less receptive for a fertilized egg to implant.
Factors That Affect Ovulation Prevention
While combination birth control pills are highly effective, inconsistent use can reduce their ability to prevent ovulation. Missing pills or taking them significantly later than the scheduled time can lead to a drop in hormone levels, potentially allowing the body’s natural ovulatory cycle to resume. The hormones in birth control pills typically wear off in about 36 hours, so consistent daily intake is important to maintain suppression.
Certain medications and herbal supplements can interfere with the effectiveness of birth control pills. Some anti-seizure medications (e.g., carbamazepine, phenytoin, and topiramate) can increase the breakdown of birth control hormones in the liver, making them less effective. The antibiotic rifampin, used to treat tuberculosis, is known to reduce hormone levels, increasing the risk of pregnancy. Herbal supplements like St. John’s Wort can also induce enzymes that metabolize birth control hormones, potentially leading to reduced effectiveness and breakthrough bleeding. It is always advisable to discuss all medications and supplements with a healthcare provider or pharmacist to identify potential interactions.
It is important to distinguish between different types of birth control pills. Combination pills primarily prevent ovulation, offering consistent suppression of the ovarian cycle. Progestin-only pills, sometimes called mini-pills, primarily work by thickening cervical mucus and thinning the uterine lining. While they can sometimes suppress ovulation, this effect is not as consistent as with combination pills, meaning ovulation may still occur in some cycles, though pregnancy risk remains low due to other mechanisms.
What to Do If You Suspect Ovulation
If you suspect ovulation or are concerned about the pill’s effectiveness, there are practical steps you can take. While on the pill, typical ovulation signs like a surge in cervical mucus or ovulation pain are usually suppressed. However, if you experience unusual symptoms such as unexpected changes in cervical mucus, mild cramping, or breast tenderness, it warrants attention.
If you have missed one or more pills, or are taking medications that might interact with your birth control, use a backup method of contraception, such as condoms. For combination pills, if you miss two or more, use backup contraception for at least seven days. For progestin-only pills, a missed pill is generally considered if it’s been more than three hours past your usual time, and backup contraception is recommended for the next 48 hours.
If you have had unprotected sex after a suspected missed pill or drug interaction, considering emergency contraception might be appropriate. Consult a healthcare provider or gynecologist for personalized advice. They can assess the situation, address concerns about potential pregnancy, and discuss whether your current birth control method is still the most suitable option. Taking a pregnancy test is also advisable if conception is a possibility.