The birth control shot, known as Depo-Provera, is an injectable form of contraception to prevent pregnancy. This method relies on a synthetic hormone called progestin (medroxyprogesterone acetate), which is similar to the progesterone naturally produced by the body. The progestin works by primarily inhibiting ovulation, stopping the ovaries from releasing an egg.
In addition to preventing ovulation, the shot thickens the cervical mucus, making it difficult for sperm to reach an egg. It also thins the uterine lining, making it less receptive to a fertilized egg. Administered consistently every 12 to 13 weeks, Depo-Provera is up to 99% effective with perfect use.
Impact of a Missed Shot
Missing a Depo-Provera injection can compromise its effectiveness and increasing pregnancy risk. Protection lasts 12 to 13 weeks, sometimes up to 14. If more than 13 to 15 weeks pass since the last injection, the shot is considered missed and unreliable.
Lower progestin levels increase pregnancy risk. When levels drop, the shot’s inhibitory effects diminish. This allows ovaries to resume ovulation. Cervical mucus may also thin, making sperm travel easier, and the uterine lining might thicken, favoring implantation.
Perfect use is highly effective, but typical use (including missed shots) is about 94% effective. This means 4 to 6 out of 100 users may become pregnant within a year. Hormone fluctuations from a missed shot can also cause irregular spotting.
Immediate Steps to Take
If you realize you have missed or significantly delayed your birth control shot, the most important immediate step is to contact your healthcare provider. They can offer personalized guidance based on how late you are for your injection and your individual circumstances. Your provider will help determine the best course of action to restore contraceptive protection.
It is important to immediately use a non-hormonal backup contraception method, such as condoms, if you engage in sexual activity. This is necessary to prevent pregnancy until your protection from the shot is re-established. Continue using backup methods even after receiving a delayed injection, as the shot needs time to become fully effective again.
If unprotected sexual intercourse has occurred within the past 120 hours (five days) and your shot is significantly delayed, discussing emergency contraception with your healthcare provider is advisable. Your provider will also likely require a pregnancy test before administering your next dose to ensure you are not pregnant.
Resuming Your Schedule
After a missed shot, your healthcare provider will guide you on how to resume your injection schedule. This often involves receiving the next injection as soon as possible, typically after a negative pregnancy test to confirm you are not pregnant. The timing of this next shot will depend on how long it has been since your last injection.
Following a delayed injection, it is generally recommended to continue using a backup method of contraception for at least seven days. This allows sufficient time for the progestin levels to rise and for the contraceptive effects, such as ovulation suppression and cervical mucus thickening, to be fully re-established. Your provider will confirm the exact duration for backup contraception.
You might experience changes in your menstrual bleeding patterns after a missed shot and subsequent re-initiation of Depo-Provera. Irregular bleeding or spotting is a common side effect, particularly during the first year of use, and can be influenced by fluctuations in hormone levels. With consistent future use, many individuals experience lighter periods or even a complete cessation of periods (amenorrhea). Adhering to the regular 12 to 13-week injection schedule is important to maintain consistent protection and minimize such irregularities.