How Home Pregnancy Tests Work
A home urine pregnancy tests is manufactured to detect the presence of hCG in the urine. Although this test will not be able to provide the actual level of hCG, it nevertheless determines if this hormone is present. A positive result means that the woman’s body is producing hCG.
The home pregnancy test is used by urinating on the test strip. Different tests on the market will have different positive pregnancy alerts on them. Some “results windows” may show a double line, others will show a plus sign, and still others will show a happy face. Regardless of what the sign is, these positive results are caused by the hCG reacting with monoclonal antibodies in the tester.
There should also be a second window on the test called the “control indicator.” A line will always appear in this box to make sure that the test is working properly. If a line does not appear in this box, then re-testing may be necessary.
Many home pregnancy tests will recommend that a second test should be done two or three days later to ensure that the result is accurate. This is generally recommended if the testing is done too early, which may result in a false negative.
What are the pros and cons of home pregnancy tests versus blood tests to confirm your pregnancy?
One of the first things that women do when they suspect they might be pregnant is purchase a home pregnancy kit. There are some drawbacks to home tests, primarily in that the results are not always accurate. Some women can have a false negative test result, which means that you could actually be pregnant when the test shows you are not. The best way to absolutely confirm your pregnancy is to have a blood test at your provider’s office. The blood test will examine even the smallest amount of hCG in the blood. For more information about hCG, see What is hCG?.
Here are some advantages as well as limitations of each pregnancy test:
Urine Pregnancy Test (Home Test)
- Immediate results
- Easy to purchase in pharmacy
- Not as accurate (false negatives are possible)
- Less expensive
- Blood Pregnancy Test
- Results may be delayed if sent to lab
- Requires a visit to provider or clinic
- More accurate
- May be covered by insurance
Home Pregnancy Tests vs. Doctor’s Office Pregnancy Tests
At the doctor’s office, pregnancy detection can be done using either blood or urine tests. Both types of test are screen for hCG hormone, which begins to gradually rise as soon as a woman becomes pregnant. Blood tests can detect hCG earlier than urine tests can.
For many women, taking a home pregnancy test confirms their suspicion that they are pregnant. A woman who receives a positive reading on a home pregnancy test should call her doctor to confirm these results. The doctor will be able to run more sensitive tests and do a pelvic exam. Detecting pregnancy as early as possible can help keep both mother and baby healthy. A woman who receives a negative reading on a home pregnancy test but still doesn’t get her period should take another test again in a few days or a week.
How do the Pregnancy Tests work?
The hormone hCG which is produced by the mother’s placenta, is measured in your urine or blood. If you are taking a home pregnancy test, be sure to follow the instructions carefully and contact the manufacturer if you have trouble reading the results. Your home test results will be more accurate if you use your first morning’s urine. Remember that if you have any questions about confirming your pregnancy, be sure to call or visit your health care provider or local clinic.
Which Test is Best?
Pregnancy is one of the most important experiences a woman can face. If a woman suspects she is pregnant because she has missed a period or because she has other symptoms the first thing she may want to do is run to a drugstore to buy a home pregnancy test. Before buying an over-the-counter pregnancy test a woman should be informed so she may purchase the test that is right for her. Not all pregnancy tests are alike.
Sensitivity to the Pregnancy Hormone
When a woman is pregnant her body begins to produce the hormone human chorionic gonadropin (hCG). This hormone tends to double every couple of days and is often able to be detected by a home pregnancy test by the time a woman has missed her period. Women who are testing close to the date of their missed period should select a test that is more sensitive to hCG. The label on the box of the home pregnancy test will usually tell at what level the test will detect the hormone. A test that detects pregnancy at 25 mLU/ml will show a woman a positive result earlier than one that detects at 50 mLU/ml.
Buy Boxes with More than One Test
All pregnancy tests run a small risk of providing a false negative result. Buying a pregnancy test with more than one test stick in the box is cost efficient because results can be double checked.
Look at Prices
Higher priced pregnancy tests are not necessarily more accurate than cheaper brands. A store brand home pregnancy test may be able to detect pregnancy earlier than a more expensive name brand if it is created to be more sensitive to lower hormone levels. It is not necessary to purchase the most expensive brand to find out if you are pregnant. Buying cheaper tests may save a woman a lot of money, especially since many women will test repeatedly to make sure the result is correct.
If a pregnancy test comes out negative but a woman feels strongly she is pregnant she should wait a few days and test again when hormone levels may be higher.
If a woman tests positive on a home pregnancy test she should make an appointment with her OB/GYN immediately as early pre-natal care is very important. A woman should also check with her doctor if she tests negative but feels strongly she is pregnant to rule out pregnancy or any other health problems.
Accuracy of Home Pregnancy Tests for Beta hCG Levels
Human chorionic gonadotropin, or hCG, is a hormone released by the growing placenta after an embryo implants. Women generally start their periods 14 days after ovulation. HCG levels in early pregnancy rise like this, on average:
- 10 days after ovulation: beta hCG level 25mIU/ml
- 12 days after ovulation: beta hCG level 50mIU/ml
- 14 days after ovulation: beta hCG level 100 mIU/ml
Virtually every early detection pregnancy test has the sensitivity to detect 100 mIU/ml of hCG, so a test will be positive by the first missed period in most cases. Most HPTs have two lines, one for a “control” and one that shows the actual result. The actual result line should be darker than the control line in a positive pregnancy test. Results show up in just a minute or two.
How to Get an Accurate Result
Home pregnancy tests are quite accurate as long as they are used properly. The first recommendation that most home pregnancy test companies suggest is to wait until the woman has missed her period. This will give the body enough time to produce enough hCG for the test to detect. If she is indeed pregnant, but her period is not due for a couple of days, the home pregnancy test may not be able to pick up on the small amount of hCG present.
It is important to read the test during the “test reading time.” A result must only be read during this time, or the result will not be accurate. A result read hours after this time will not provide an accurate result. What may be showing at this elapsed time is an evaporation line, which can occur as the urine dries on the tester.
Testing first thing in the morning is usually best since the urine is much more concentrated at this time.
Using Home Pregnancy Test Kits Correctly
To get the best results from HPTs:
- Test first thing in the morning, because the urine in the morning is most concentrated, and will give the most accurate results
- Read the tests within the time stated on the HPT. The test band may change colors and not be accurate if it isn’t read within the allotted time.
False Positives and Negatives on Home Pregnancy Tests
Everyone is different, and hCG levels aren’t exact from one women to another. A negative pregnancy test, especially if done right before or the day of a missed period, may still be positive; it might just be slightly too early. Test again in a few days (okay, a few hours), and be sure to use the first urine sample of the day.
False positives are far less common, except for the following conditions:
- Taking hCG injections for an IVF or IUI cycle ; hCG in small amounts may still be present in the urine up to 14 days, although it usually clears by day 10 after the injection.
- Miscarriage in the past month; it takes four weeks or so for the hCG levels to drop completely.