Whether it is a blood or urine test, all pregnancy tests, including in-home pregnancy kits, work the same way—by testing for the presence of human chorionic gonadotropin (hCG). hCG is a hormone produced in the placenta after egg fertilization. Its concentration doubles every 2-3 days, peaking around the eighth week of pregnancy.
Many tests can start to detect pregnancies as early as 10-15 days after conception or one day after a missed menstrual period. But since the level of hCG continues to rise, the test becomes more sensitive over time. So on the first day after a missed period, the urine pregnancy test may only detect some pregnancies, but one week later it would likely detect most pregnancies. If you tested and the result was negative, and you still have not started your period, wait a few days and test again.
It is important that you read the directions. Not all in-home pregnancy kits are used in the same way. With some kits, you will urinate in a cup and then use a dropper to place a small sample of your urine on the test area. Other kits require you to urinate directly on the test stick. The results are generally ready in under 5 minutes.
In-home pregnancy tests are very accurate if used appropriately one week or more after your missed period. However, the results are much less accurate if the test is done incorrectly, if the instructions are not followed, or you use the test too early.
It is important that you follow the directions and understand how to interpret the results. Manufacturers state that in-home pregnancy tests can be used as soon as one day after a missed period, but understand that the tests are much more accurate if you wait a week after a missed period.
When an error does occur, more often than not, it is a false-negative—meaning the test says you are not pregnant when you are. If the test result is negative but you are experiencing early signs of pregnancy, it is best to see your healthcare provider. The earlier that you begin prenatal care, the better it is for both you and your baby.
If your home pregnancy test is positive for a pregnancy, it is very likely to be correct. It is extremely rare that a test would give you a positive result if you were not really pregnant.
The most common cause of a missed period is pregnancy. But what if you have missed a period and are not pregnant? Some other causes of missed periods include but are not limited to:
American Congress of Obstetricians and Gynecologists
Office on Women's Health
The Canadian Women's Health Network
The Society of Obstetricians and Gynaecologists of Canada
Pregnancy testing. Planned Parenthood website. Available at: https://www.plannedparenthood.org/teens/going-to-the-doctor/pregnancy-testing. Accessed December 10, 2015.
Pregnancy tests. Office on Women's Health website. Available at: http://www.womenshealth.gov/publications/our-publications/fact-sheet/pregnancy-test.html. Updated December 23, 2014. Accessed December 10, 2015.
Taking a pregnancy test. American Pregnancy Association website. Available at: http://americanpregnancy.org/getting-pregnant/taking-a-pregnancy-test. Updated September 2015. Accessed December 10, 2015.
Last reviewed December 2015 by Michael Woods, MD Last Updated: 12/10/2015