The birth control shot, known as Depo-Provera, offers a highly effective and convenient method of contraception. Administered as an injection typically every three months, it releases a hormone that prevents pregnancy. Many individuals choose this method due to its long-lasting nature, eliminating the need for daily pills or other frequent actions. Despite its high effectiveness, questions about the possibility of pregnancy while using the shot are common.
How the Birth Control Shot Prevents Pregnancy
The birth control shot contains medroxyprogesterone acetate, a synthetic form of progesterone. This hormone prevents conception through several mechanisms. One key action is suppressing ovulation, meaning the ovaries do not release an egg. Without an egg, fertilization cannot occur.
The shot also thickens cervical mucus, creating a physical barrier that makes it difficult for sperm to travel through the cervix and reach an egg. Additionally, the progestin thins the uterine lining, making it less hospitable for a fertilized egg to implant and grow, further contributing to its contraceptive effect.
How Effective Is the Birth Control Shot?
The birth control shot is one of the most effective reversible methods of contraception available. When used perfectly, its effectiveness rate can be as high as 99% to 99.8%.
This means fewer than 1 in 100 individuals using the shot perfectly will become pregnant in a year. Perfect use involves consistently receiving the injection on schedule. In typical use, where factors like missed appointments occur, the shot’s effectiveness is slightly lower, ranging from 94% to 96%. This translates to approximately 4 to 6 in 100 users experiencing an unplanned pregnancy each year. To maintain its high level of protection, the birth control shot needs to be administered by a healthcare provider every 12 to 13 weeks, which is about four times a year.
Reasons Pregnancy Can Occur While on the Shot
While the birth control shot is highly effective, pregnancy can still occur. The primary reason for reduced effectiveness is not receiving the injection on its scheduled timeline. If an individual delays or misses a shot, especially if the interval extends beyond 13 to 15 weeks, contraceptive protection may diminish, increasing the chance of pregnancy. Healthcare providers advise using a backup method if an injection is significantly late.
Another factor is how the shot is initially started. If the first injection is not given within the recommended timeframe, such as within the first five days of a menstrual period or shortly after childbirth, backup contraception may be necessary for the first week. This ensures continuous protection while hormone levels build up to a contraceptive dose. Individuals might also unknowingly be pregnant at the time of their first injection, as the shot is contraindicated in known or suspected pregnancy. A pregnancy test might be conducted before the initial dose.
Some medications or herbal products can potentially interfere with its effectiveness. Certain anti-seizure drugs (e.g., carbamazepine, phenytoin, topiramate) and St. John’s Wort can reduce the hormone concentration. It is important to inform a healthcare provider about all medications and supplements to assess for any possible interactions.
Suspecting Pregnancy While on the Shot
Even with effective contraception, it is natural to be concerned about pregnancy if new bodily changes occur. Common signs include nausea, breast tenderness, fatigue, and increased urination. While a missed period is a typical pregnancy symptom, many on the birth control shot experience irregular bleeding or no periods, making this sign less reliable.
If concerned about pregnancy, taking an at-home pregnancy test is a first step. These tests detect human chorionic gonadotropin (hCG), a hormone produced during pregnancy, and their accuracy is not affected by the shot’s hormones. For accurate results, it is recommended to take a test after a missed period or approximately 21 days after potential conception.
Regardless of the at-home test result, consult a healthcare provider promptly if pregnancy is suspected. They can provide confirmation through clinical testing and offer guidance. Consulting a medical professional ensures appropriate care and advice.