Home pregnancy tests can find the presence of a pregnancy hormone (called human chorionic gonadotropin, or hCG) in a sample of urine. High levels of hCG are made during pregnancy. The home tests have similar results to the pregnancy tests done on urine in most doctors' offices if they are used exactly as instructed.
When a woman becomes pregnant, the egg is generally fertilized by a sperm cell in a fallopian tube (conception). Within 9 days after fertilization, the egg moves down the fallopian tube into the uterus and attaches (implants) to the wall of the uterus. When the fertilized egg implants, the placenta starts to develop and begins to release hCG into the woman's blood. Some of this hCG also passes in her urine. In the first few weeks of pregnancy, the amount of hCG in the urine gets higher very quickly—it doubles every 2 to 3 days.
There are two basic types of home pregnancy tests.
- The most common types of home pregnancy tests use a test strip or dipstick that you hold in the urine stream or dip into a sample of urine.
- A second type uses a urine collection cup with a test device. To use this type of test, you may place several drops of urine into a well in the test device or you put the test device into urine collected in a cup.
The accuracy of home pregnancy tests is different for every woman because:
- The days of a woman's menstrual cycle and ovulation can change each month.
- The exact day of implantation of the fertilized egg is not always known.
- Each home pregnancy test kit has a different sensitivity to find hCG.
While a few home pregnancy tests may be sensitive enough to show a pregnancy on the first day of a woman's missed period, most test kits are more accurate about a week after a missed period.
Why It Is Done
A home pregnancy test is done to detect pregnancy by detecting human chorionic gonadotropin (hCG) in your urine.
How To Prepare
You can buy home pregnancy test kits at the drugstore or grocery store. You don't need a prescription.
The test kits generally have plastic dipsticks or test strips and instructions that explain how to do the test. Some kits have a urine collection cup and a dipstick that you dip in urine. Midstream kits have a test strip that you hold in your stream of urine for several seconds. All kits tell you to wait a specific amount of time before reading the results.
When to test
Home pregnancy kits can be used on the first day of a missed menstrual period. But the test results are more accurate if you wait a few days longer. If you do the test as soon as you have missed a period and the results show you are not pregnant (negative results), repeat the test in 1 week if your menstrual period has not started, or have a pregnancy test done at your doctor's office or a clinic.
For any home test, you should follow some general guidelines:
- Check the expiration date on the package. Do not use a test kit after its expiration date—the chemicals in the kit may not work correctly after that date.
- Read the instructions that come with your test carefully and thoroughly before doing the test.
- Follow the directions exactly. Do all the steps, in order, without skipping any of them.
- If a step in the test needs to be timed, use a clock. Do not guess at the timing.
How It Is Done
Carefully read the instructions that come with the home kit. Instructions vary from kit to kit. Be sure to read the result at the appropriate time indicated in the instructions for accurate results.
If you have a kit that asks for a morning urine sample, test urine that has been in the bladder for at least 4 hours. Test the urine within 15 minutes of collecting the sample.
If you are using a midstream kit, urinate a small amount first and then hold the dipstick in your urine stream as you finish urinating. Test the urine sample according to the directions included in the test kit package.
How It Feels
There is no pain or discomfort in doing a home pregnancy test.
There are no problems with collecting a urine sample for a home pregnancy test. But there may be a chance that you read the results wrong. With any home pregnancy test, if the test shows you are pregnant (positive test), you should see your health professional to confirm the test and arrange follow-up care. If the test does not show you are pregnant (negative test), it is still possible that you may actually be pregnant. You should repeat the test in 1 week if your menstrual period has not started. If the repeat test is negative, probably you are not pregnant, but you should talk to your health professional about why you are not having periods.
Home pregnancy tests can find the presence of a pregnancy hormone (called human chorionic gonadotropin, or hCG) in a sample of urine. If you are pregnant, most tests show a symbol in the indicator area of the test strip or on the part of the test device.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Taking the test very early in your pregnancy. HCG may not be found. In this case, the test kit may show that you are not pregnant when you really are pregnant. This is called a false-negative result. If you have drunk a lot of fluid, your urine may be diluted and this may also cause a false-negative result.
- Certain things may cause the test results to show that you are pregnant when you are not pregnant. This is called a false-positive result. False-positive results may be caused by reading the test at the wrong time or having hCG hormone in the urine from some other cause.
- Not reading the result at the right time as shown on the instructions. If you read the result too early or too late, the colour change may not be accurate, and you will need to retest.
What To Think About
- Some home pregnancy tests are easier to use and read than others. Be sure to follow the instructions exactly for accurate results.
- Human chorionic gonadotropin (hCG) can be found in the blood before it can be found in the urine. A blood test can confirm a pregnancy about 6 days after the fertilized egg implants into the uterus (even before a missed menstrual period). To learn more, see the topic Human Chorionic Gonadotropin (hCG).
- Many women are able to tell if they are pregnant simply by knowing their body has changed. A missed menstrual period, breast tenderness, morning nausea, and fatigue may be early signs of pregnancy. But a home pregnancy test can confirm pregnancy when a menstrual period is late.
- Some health professionals may want to do another pregnancy test in their labs to confirm the pregnancy before beginning prenatal care.
- If you are thinking of becoming pregnant, think about making changes in your nutrition (such as avoiding alcohol and taking a vitamin containing folic acid) to lower the chance of birth defects. Good nutrition before and during your pregnancy helps your health and the health of your baby.
- If you are thinking of becoming pregnant, try to find your most fertile time (ovulation). This can be checked in several ways. To learn more, see the topic Fertility Awareness. Ovulation test kits may help you know your most fertile time. These are available without a prescription in supermarkets and pharmacies.
- Confirming your pregnancy early can be very useful. It allows you to start prenatal care during the first month of pregnancy. Or, if the pregnancy is unplanned, you can talk with your health professional about other choices.
Some common questions about home pregnancy tests
- Why did I see a faint positive line an hour after I did the test? You may be pregnant but your hCG level may not be high enough in your urine. Take another test in a few days or talk to your health professional about a blood test.
- Why was my test positive right before I started my menstrual cycle? This could be a sign of an ectopic (tubal) pregnancy or a miscarriage. If you get a positive test right before your menstrual period, call your doctor or midwife right away.
- Can I be pregnant but get a negative test? Yes, most women will get a positive test within a few days of missing their menstrual period but some women may get a negative test early in their pregnancy.
- Can alcohol or drugs change the test? Most test results are not affected by alcohol or drugs, but you should not use these substances if you want to become pregnant or think you may be pregnant.
Other Works Consulted
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Current as of: May 29, 2019
Author: Healthwise Staff
Sarah Marshall MD - Family Medicine
Brian D. O'Brien MD - Internal Medicine
Adam Husney MD - Family Medicine
Kathleen Romito MD - Family Medicine
Rebecca Sue Uranga