How pregnancy tests work
Think you might be pregnant?
Even with the most effective birth control methods, there’s always a chance for error. After all, it takes just one sperm to fertilize the egg. Finding out whether or not that’s happened is as easy as taking an over-the-counter (OTC) pregnancy test.
OTC pregnancy tests typically test your urine for a hormone called human chorionic gonadotropin (HCG). HCG is only present if you’re pregnant. The hormone is only released if a fertilized egg attaches outside the uterus or to your uterine lining.
There are different ways to collect your urine for the test. Depending on the test you choose, you may have to:
- collect your urine in a cup and dip a testing stick into the liquid
- collect your urine in a cup and use an eyedropper to move a small amount of fluid into a special container
- place the testing stick into the area of your expected urine stream so that it will catch your urine midstream
According to Cleveland Clinic, most tests are 99 percent effective if taken after a missed period. The best part is that you can do it in the privacy of your own home. Simply open the test, follow the instructions, and wait for the recommended amount of time to view the results.
After the recommended waiting time has passed, the tests will display your results in one of the following ways:
- a change in color
- a line
- a symbol, such as plus or minus
- the words “pregnant” or “not pregnant”
How soon can you take a pregnancy test?
You should wait to take a pregnancy test until the week after your missed period for the most accurate result.
If you don’t want to wait until you’ve missed your period, you should wait at least one to two weeks after you had sex. If you are pregnant, your body needs time to develop detectable levels of HCG. This typically takes seven to 12 days after successful implantation of an egg.
You may receive an inaccurate result if the test is taken too early in your cycle.
Here are some signs that you should take a pregnancy test.
1. You’ve missed your period
One of the first and most reliable signs of pregnancy is a missed period.
If you don’t track your cycle closely, it might be hard to determine whether or not you’re late. Many women have a 28-day menstrual cycle. Consider taking a test if it’s been more than a month since your last period.
Keep in mind that your period can sometimes be delayed or skipped due to stress, diet, exercise, or certain medical conditions.
Also pay attention to your flow if you suspect pregnancy. It’s common to experience light bleeding or spotting in the early weeks as the egg buries deeper into the uterine lining during implantation. Take note of any difference in the color, texture, or amount of blood.
Contact your doctor if you have bleeding and a positive pregnancy test.
2. You have cramps
Implantation can also produce a feeling similar to menstrual cramps. In early pregnancy, you may feel this discomfort and think your period is just around the corner, but then it never comes.
Sound familiar? Take a test. Hormone levels vary by woman and by pregnancy.
3. Your breasts hurt
As your pregnancy produces more and more estrogen and progesterone, these hormones start to make changes in your body to support the baby’s growth.
Your breasts may feel tender and appear bigger due to increased blood flow. Your nipples might hurt and the veins might look darker under the skin.
Because many women also experience breast discomfort in the days leading up to their period, this symptom isn’t always indicative of pregnancy.
4. You’re feeling different
Along with cramps and sore breasts, early pregnancy can cause:
- food aversions
- frequent urination
As the weeks go on, these symptoms may get stronger before your HCG levels even out late in the first trimester. You know yourself, so pay attention to your body. Any unusual physical symptoms could prompt you to take a pregnancy test.
5. Your contraception failed
Birth control pills, condoms, and other types of contraceptive devices don’t provide 100 percent protection from pregnancy. In other words, there’s always a slight chance of pregnancy, no matter how careful you are.
Despite your birth control preferences, consider taking a test if you experience any of the signs we’ve listed.
Human error or defects can also result in unplanned pregnancy. Birth control pills can be difficult to remember to take each day. According to Planned Parenthood, 9 out of every 100 women on the pill will get pregnant if they don’t take it as directed.
Condoms can break and tear or otherwise be used incorrectly. According to Planned Parenthood, nearly 18 in every 100 women relying on condoms for contraception get pregnant each year.
If you’re worried about contraceptive failure, ask your doctor about alternative contraceptive methods, such as an intrauterine device (IUD). According to Planned Parenthood, less than one out of every 100 women using an IUD gets pregnant each year.
When in doubt, test!
Sexually active women in their reproductive years have a chance of pregnancy every month, even when using protection. There are certain signals your body might send that should prompt you to take a pregnancy test.
For the best results, take the test after you think you’ve missed your period. Test during your first morning bathroom visit, or hold it for several hours to increase the concentration of the HCG hormone that the test measures.
Testing early helps to ensure that you get proper care for yourself and, if applicable, prenatal care for your baby. In the event of a positive result, contact your doctor as soon as possible to discuss your options and potential next steps.
Q&A: How accurate are at-home pregnancy tests?
How accurate are at-home pregnancy tests?
Home pregnancy tests (HPTs) are quite accurate. They work by detecting the presence of human chorionic gonadotropin (hCG) in the urine, which is produced when pregnancy occurs. However, different brands of tests are able to recognize different amounts of the hormone. Levels of hCG are very low in the beginning of a pregnancy, causing some HPTs to give a false negative result. If you get a negative result and still don’t have your period within a few days, you should retest.
Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.