Approximately every month, most sexually active women of child-bearing years could become pregnant. During ovulation, an egg is released from the ovary and makes its way to the uterus. If it is fertilized by a sperm and implants on the uterine wall, a woman is pregnant. If she is not pregnant, the lining of the uterus sheds (this is your period), and the cycle repeats.
Pregnancy tests are most accurate about one week after a missed period.
When a fertilized egg attaches itself to the uterine wall, the body begins producing a hormone called human chorionic gonadotropin, or hCG. The levels of this hormone rise rapidly in early pregnancy, almost doubling every two to three days. hCG is detectable in urine and blood, and is a sign of pregnancy.
There are different types of pregnancy tests available. Home pregnancy tests, which you can buy in drugstores, test for hCG in urine. Blood tests done in a health provider’s office don’t just test for the presence of hCG, which indicates you are pregnant, but also can tell how much hCG is present. Measuring hCG levels helps a provider determine how far along you are, if you have more than one developing embryo, or if there might be a problem with the pregnancy.
Those who suspect they may be pregnant can use home pregnancy tests to find out if they are pregnant as soon as one week after a missed period. Although some products advertise that they give results earlier than that, most experts agree accuracy is best if you wait to test after the egg has implanted, or about one week after your missed period. These tests are convenient, private, easy to use, inexpensive, and about 99 percent accurate if used properly.
To use home pregnancy tests with best results, follow the instructions on the package you purchase as closely as possible. Most require you to place the test stick in your urine, wait a few minutes, and then read the results on the stick display. Some tests are digital and clearly say pregnant or not pregnant, while other tests require you to read lines or plus-or-minus signs to indicate pregnancy. Accuracy of the test depends on:
- how well you follow the instructions in the test’s packaging
- how soon after you are actually pregnant that you take the test
- when you ovulated and if an egg has implanted
- sensitivity of the test
When you take a home pregnancy test, also check the expiration date on the package and do not use it if the date has passed. Also, if you want to confirm the test results, it’s a good idea to wait a couple of days and then take the test again, especially if the first test was negative for pregnancy. It’s still possible you may be pregnant. Test kits may include one or more tests in a package, and range from less than $10 to around $15. There are name brands, such as Clear Blue Easy and First Response, and also generic store brands available.
It’s possible to have a false-positive result, which is rare and might indicate you have an ectopic pregnancy or are menopausal. You can have false-negatives, too. These are more likely than false-positives and may be due to taking the test too early, checking your test results too soon, or having very diluted urine. It’s best to take the test the first thing after waking up to minimize the possibility of your urine being too dilute.
Most medications do not interfere with the results of your test, and that includes antibiotics and birth control pills. But some fertility drugs and medications containing hCG may affect the results of the test.
If you have a positive test, make an appointment with a health care provider to verify your results. Good prenatal health care ensures the best outcome for you and your developing baby. Planned Parenthood is a good resource for pregnancy testing and information on prenatal health.