Home Pregnancy Tests: Are they accurate?

By Eileen Bailey

Home pregnancy tests have become commonplace. A woman can find out if she is pregnant within minutes and anytime of the day or night. Some tests boast they can detect a pregnancy the first day of a missed period. But how accurate are these tests? Can you really know if you are pregnant the day you should have gotten your period?

Two Types of Pregnancy Tests

There are two basic types of pregnancy tests: blood tests and urine tests. Both tests determine pregnancy by detecting the presence of human chonrionic gonadotrophin (hCG), the hormone that is present in a woman only after an embryo attaches itself to the uterine wall. Once this happens, hCG levels rise quickly and continue to rise each day.

Blood tests must be completed by a doctor and are typically more accurate than urine tests. Blood tests can normally detect pregnancy as early as six to eight days after ovulation. This is because blood tests can detect a very small amount of hCG. A quantitative blood test will measure the exact amount of hCG and is helpful in determining date of conception. A qualitative blood test will simply look for the presence of hCG and give a "yes" or "no" answer.

Urine tests detect hCG when they rise above a certain level. Because of this, they are not normally able to detect pregnancy as early as a blood test can, however they can sometimes detect pregnancy as early as the first day of a missed period. Home pregnancy tests are urine based pregnancy tests.

Accuracy of Home Pregnancy Tests

Most home pregnancy tests are very accurate. Although many home pregnancy tests claim 99% accuracy on the first day of a missed period, a study completed in 2004 ["Pregnancy Tests", 2006, National Women's Health Information Center] found only one brand of test (First Response, Early Result Pregnancy Test) consistently detected the small amounts of hCG present that early. Even so, home pregnancy tests are considered accurate, especially when used one week after a missed period.

Using a Home Pregnancy Test

There are several factors that contribute to the accuracy of home pregnancy tests:

Following Directions - Each brand of test may have different instructions for use. There may be different waiting times or different methods for collecting urine. To help ensure accuracy, be sure to read and follow all directions on the package. Checking the expiration date to make sure the expiration date has not passed is also important.

Using after One Week- Although most tests claim accuracy the day of a missed period, research has shown tests are more accurate when used one week after a missed period. In addition, using the test the first thing in the morning can make the test more accurate than if used later in the day.

The Brand of Test-There are many different home pregnancy tests available on the market today. Some are more sensitive to detecting low levels of hCG and would be more able to detect pregnancy early. Most tests, however, are accurate within one to two weeks of a missed period. First Response, Early Result Pregnancy Test was found in a study to be the most accurate test as early as the first day of a missed period.

In addition, women's bodies may react to pregnancy differently. Some women may take longer for the fertilized egg to be implanted on the wall of the uterus. The hormone hCG is not present until this happens. In addition, some women may have lower amounts of hCG and, therefore, pregnancy will take longer to detect.

Negative Results

If you receive a negative result from a home pregnancy test and you believe you may be pregnant, it is suggested you retake the test several days to one week later. It may be that you have attempted to take the test too early

If you believe you are pregnant, it is important to contact your doctor. The sooner you begin receiving pre-natal care and taking care of yourself and your baby, the better chance you have of having a successful pregnancy and a healthy baby.

References:

"Pregnancy Tests", 2006, national Women's Health Information Center, U.S. Department of Health and Human Services

"Pregnant or Not? How to Know" 2007, Melissa Stoppler, M.D., Medicinenet.com