While the risk of pregnancy on hormonal birth control is low, recognizing the signs of an unplanned pregnancy can be more challenging. The side effects of hormonal birth control may mimic the symptoms of early pregnancy, including breast tenderness, weight gain and nausea. Fortunately, hormonal contraceptives do not change the efficacy of either urine- or blood-based pregnancy tests.
Hormonal birth control works in three different ways, according to Planned Parenthood. First, the hormones in your birth control suppress ovulation. They thicken cervical fluid, creating a physical barrier at the mouth of the uterus. Finally, they thin the uterine lining, making the environment of the uterus unable to support pregnancy. All forms of hormonal birth control function in the same three ways to prevent pregnancy.
The most common early sign of pregnancy is a missed period. If you use the birth control shot or the progesterone-only mini-pill, you may miss periods and experience irregular bleeding as a side effect of the hormones. You can also skip periods on combination estrogen and progesterone birth control if you take pills without a spacer week or placebo pills. In either situation, a missed period is not a cause for alarm; however, if you take a standard combination birth control pill and do not have a period during your week of placebo pills, you may want to take a pregnancy test.
Common symptoms of early pregnancy include breast tenderness, bloating, nausea and fatigue. If you have recently started hormonal contraception, these are also typical side effects associated with most of these types of birth control. Should these symptoms appear after you have been on birth control for some time, a pregnancy test may be appropriate.
Before you panic, think about your birth control. If you have taken your combination birth control pills daily at around the same time, changed your patches or used your vaginal ring appropriately, the risk of pregnancy is less than 1 percent, according to the Mayo Clinic. Even if you’ve missed a single pill, the risk is still quite low. Take a deep breath, relax and make sure you know what to do if you do miss a pill.
While a missed period is typically one of the most noticeable signs of pregnancy, some women do experience bleeding while pregnant. Implantation bleeding, or light spotting when a fertilized egg implants in the uterine lining, often occurs around when you would expect your period. Light periods are common on many forms of hormonal birth control, but you may want to test for pregnancy if your period is much lighter than normal or you only experience pink or brown spotting.