Home and Clinic Pregnancy Tests
What Is a Pregnancy Test?
Pregnancy tests detect a hormone called human chorionic gonadotropin (hCG) in a sample of urine or blood. This hormone is produced by the placenta after conception and is found only in pregnant women. The amount of hCG produced during early pregnancy doubles every two or three days and levels off in the second or third month. You can be tested for pregnancy with an over-the-counter pregnancy test or in your healthcare provider's office.
How Soon After Conception Will a Home Pregnancy Test Work?
Some home pregnancy tests can detect pregnancy as early as six days after conception, or one day after a missed menstrual period. Home pregnancy tests are most accurate if you wait two weeks after your first missed menstrual period.
How Are Pregnancy Tests Done at Home?
Follow the directions carefully as they differ with different brands. Some require that you urinate directly on a stick, while others ask that you urinate in a cup and place a small sample into a testing well with a dropper. You will know the results in two minutes to several hours. Results are displayed differently with different tests. For example, some show a red plus or minus sign in a window, others show pink or blue lines on a test strip, while others change the color of a urine sample.
How Accurate Are Pregnancy Tests?
Home pregnancy tests are never 100% accurate. Many manufacturers claim to have a 99% accuracy rate, but inaccurate results may be more frequent due to improper use of the test, using the test after its expiration date, exposure of the test to the sun, and other factors. The procedures outlined in the instructions must be followed exactly for the results to be accurate. Whatever the result or the brand used, most manufacturers recommend repeating the process several days later to confirm the results. After conception, a woman produces a minimal amount of hCG. The strength of each test varies, and although a woman may be pregnant, the test may not pick up the amount of hCG hormone present the first time.
You may get a negative test even if you are pregnant (false negative) if you:
- Take the test too early after conception, before hCG levels are significant
- Are taking diuretics or promethazine (an antihistamine)
You may get a positive test even if you are not pregnant (false positive) if you:
- Are taking anticonvulsants, anti-Parkinson drugs, hypnotics, or tranquilizers
- Have blood or protein in the urine
How Are Pregnancy Tests Conducted in a Medical Office?
A more reliable pregnancy test—either a urine test or blood test—is available at your health care provider's office or a family planning clinic. An hCG urine test can be ordered as early as 10 days after a missed menstrual period. For the urine test, a urine sample is taken first thing in the morning. A blood hCG test involves taking a sample of blood from a vein in the arm. A blood test may be ordered to measure how much hCG is in the blood, which is often used to evaluate an ectopic pregnancy . Results of these pregnancy tests may be available the same day they are administered.
The National Women's Health
The National Women's Health Information Center website. Available at: http://www.4women.gov/ .
Last reviewed July 2007 by Ganson Purcell Jr., MD, FACOG, FACPE
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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