When taking a home pregnancy test, questions often arise about the results of the test, regardless of whether they are positive or negative. One common question many women have is about the impact of birth control pills on the results of a pregnancy test. Can birth control pills cause false results? Can a woman get pregnant while taking birth control pills?
How a pregnancy test works
A home pregnancy test works by indicating the presence of a hormone called human chorionic gonadotropin, or hCG, in a woman's urine. The placenta begins to produce hCG shortly after the embryo implants in the uterus, and the hormone reaches detectable levels for most women by the time her period is due.
To take the test, urine is placed on an absorbent pad with a dropper, by dipping the pad in collected urine, or by holding the pad in the urine stream. The urine then is wicked up through the pad, passing a strip of dye that reacts to the hCG present in a pregnant woman's urine. There will always be one line that develops on a pregnancy test regardless of whether or not the test is positive. This is the "control" line, and its purpose is to ensure the user that the test is working correctly. In a positive test, a second line or a plus sign will appear in the allotted time for the test. The allotted time varies between brands and your test should not be read before or after this time.
How birth control pills work
Birth control pills work by altering the normal levels of estrogen and progesterone in a woman's body. These two hormones control ovulation, or the release of an egg from her ovaries. When ovulation does not occur, a woman cannot become pregnant.
Can birth control pills cause a false positive pregnancy test?
Because birth control pills work with hormones that are present in every woman's body at all times and a pregnancy test only detects a single hormone that is specific to pregnancy, birth control pills can not cause a false-positive pregnancy test. According to the National Institutes of Health, the design and chemical specificity of a pregnancy test makes it impossible for birth control hormones to cause a false positive.
Can I get pregnant while taking birth control pills?
According to Planned Parenthood, birth control pills are considered 99 percent effective when they are taken correctly. So, one out of every one hundred women who take birth control pills will get pregnant while taking them as prescribed.
However, many women have trouble remembering to take them at the same time every day, or may take them with other medications that interfere with their effectiveness, such as antibiotics. Or, they may have other medical conditions that prevent birth control pills from limiting a woman's fertility. In these instances, pregnancy can occur.
Do birth control pills effect when I can test for pregnancy?
You may take a home pregnancy test any time you suspect that you may be pregnant. However, the chances for a false negative will be reduced if you wait until the day you would normally expect your period to start. Taking the test before this day can give you a positive if indeed you are pregnant, but you may get a false negative if you have not had enough time between conception and testing for the hCG to build up to detectable levels in your blood stream.
If you are taking birth control pills, your pill pack should tell you when to expect your period. However, some birth control pills limit the number of periods that you have during a year. If you suspect that you may be pregnant while taking these types of pills, testing 12 to 14 days after you suspect conception should give you a reliable positive or negative result.
- American Pregnancy Association; Understanding Pregnancy Tests: Urine and Blood
- Planned Parenthood; Birth Control Pill
- National Institutes of Health; A Thin Blue Line: The History of the Pregnancy Test
- Pee on A Stick:A Comprehensive Collection of Home Pregnancy Test Information and Images
- National Instiutes of Health; A Thin Blue Line: The History of the Pregnancy Test