Birth Control's Effect on Pregnancy Tests

By Erica Loop
A positive pregnancy test may mean your birth control failed.

You take your birth control pill every day, but now you think you may be pregnant and you are wondering how the pills could affect a pregnancy test. The hormones in birth control pills shouldn’t impact the level of the pregnancy hormone human chorionic gonadotropin in your blood and urine, meaning that a positive test result is not likely to be false.

Medications and HCG

Some medications can affect pregnancy tests, but birth control pills typically don't cause a false positive. The primary culprits behind false positive pregnancy tests are fertility hormones. Pregnancy tests measure hCG, so a medication that contains hCG may cause a false positive, according to the U.S. Department of Health and Human Service’s Office on Women’s Health. These medications are used for fertility treatments -- not for birth control.

Other False Positives

Even if you aren't on fertility medications you can still have a false positive that has nothing to do with your hormonal birth control. Other drugs and conditions can also cause false pregnancy test results. While false positives aren’t common, they can result from medications such as methadone, a recent miscarriage, a test error or diseases that cause your body to excrete hCG. Diseases and conditions that may cause hCG excretion include colon and cervical cancers and tubo-ovarian abscesses. You should always consult a medical professional after having a positive pregnancy test. Your doctor can determine whether the test is true or false and provide further testing if it is indeed a false positive.

Hormone Measurement

While birth control does contain hormones, it does not contain hCG, the hormone a pregnancy test looks for. Birth control implants, injections and IUDs all contain progestin while oral contraceptives, patches and vaginal rings contain combinations of progestin and estrogen. Both blood and urine pregnancy tests measure only the level of the hCG hormone in your body. This means that the level of progestin and estrogen in your body due to birth control won't affect a pregnancy test.

Birth Control Effectiveness

Faced with a positive pregnancy test, you should consult your primary care provider prior to discontinuing use of your contraceptive. Over-the counter pregnancy tests are not always accurate, according to the Centers for Disease Control and Prevention. A physician will be able to take a blood test that will tell you definitively if you are pregnant. Birth control isn’t always effective. The injection has a 6 percent failure rate and the pill, patch and ring all have 9 percent failure rates, according to the CDC.

About the Author

Based in Pittsburgh, Erica Loop has been writing education, child development and parenting articles since 2009. Her articles have appeared in "Pittsburgh Parent Magazine" and the website PBS Parents. She has a Master of Science in applied developmental psychology from the University of Pittsburgh's School of Education.