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Home pregnancy tests: Can you trust the results?

Could medications interfere with test results?

Fertility drugs or other medications that contain HCG may interfere with home pregnancy test results. But most medications — including antibiotics and birth control pills — don't affect the accuracy of home pregnancy tests.

Could a positive result be wrong?

Although rare, it's possible to get a positive result from a home pregnancy test when you're not actually pregnant. This is known as a false-positive. A false-positive may happen if you were recently pregnant or you take a pregnancy test too soon after taking a fertility drug that contains HCG. Ovarian cysts, ectopic pregnancy or menopause also may contribute to misleading test results.

Could a negative result be wrong?

It's possible to get a negative result from a home pregnancy test when you're actually pregnant. This is known as a false-negative — and it's much more likely to occur than is a false-positive. You may get a false-negative if you:

  • Take the test too early. Wait to take the test until your period is at least one day late. That's the earliest most home pregnancy tests can detect pregnancy. For the most accurate results, take the test one week after a missed period — when the level of HCG in your urine is most likely to be detectable.
  • Time the test wrong. Be sure to give the test time to work, but not too much time. Consider setting a timer according to the package instructions.
  • Use diluted urine. Drinking too much fluid before taking a home pregnancy test may cause a false-negative result. For the most accurate results, take the test first thing in the morning — when your urine is the most concentrated.

What happens next?

If your home pregnancy test is positive — or if you've taken a few home pregnancy tests and gotten mixed results — make an appointment with your health care provider. You may need a blood test or pelvic exam to confirm your pregnancy. The sooner your pregnancy is confirmed, the sooner you can begin prenatal care.

If your home pregnancy test is negative, repeat the test in a few days — especially if you took the test shortly after a missed period or your period is more than a week late. If you continue to get negative test results but your period doesn't begin, check with your health care provider. Many factors can lead to missed periods, including illness, stress, excessive exercise and hormonal imbalances. If you're not pregnant, your health care provider can help you get your menstrual cycle back on track.

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References
  1. Bastian LA, et al. Diagnosis and clinical manifestations of early pregnancy. http://www.uptodate.com/home/index.html. Accessed July 12, 2010.
  2. Months 1 and 2 (weeks 1-8). Your Pregnancy and Childbirth: Month to Month. 5th ed. Washington, D.C.: American College of Obstetricians and Gynecologists; 2010:18.
  3. Home pregnancy tests. The National Women's Health Information Center. http://www.womenshealth.gov/faq/pregnancy-tests.cfm. Accessed July 12, 2010.
  4. Cole LA. New discoveries on the biology and detection of human chorionic gonadotropin. Reproductive Biology and Endocrinology. 2009;7:8.
  5. Welt CK, et al. Etiology, diagnosis, and treatment of secondary amenorrhea. http://www.uptodate.com/home/index.html. Accessed July 12, 2010.
  6. Fact Plus (product insert). Cincinnati, Ohio: Procter & Gamble; 2008.
  7. First Response Pregnancy (product insert). Princeton, N.J.: Church & Dwight Co., Inc.; 2003.
  8. Clearblue Easy (product insert). Waltham, Mass.: Inverness Medical, Inc.; 2006.
PR00100 Oct. 30, 2010

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