One of the most nerve-wracking and exciting medical assessments, a pregnancy test is experienced by most women at least once in their lives. Fortunately, the test itself is a fairly simple process, even if the implications of the results aren't.
How Pregnancy Tests Work
Most pregnancy tests check for the presence or absence of a chemical known as human chorionic gonadotropin (hCG). Also known as the "pregnancy hormone," hCG is produced by the placenta – the uterine lining that supports and nourishes a fetus as it develops. The placenta doesn't actually exist until a fertilized egg implants on the uterine wall, so tests that look for hCG are reliable only after the fetus has implanted, six days to two weeks into a pregnancy. The levels of hCG continue to rise as the pregnancy progresses.
Other types of pregnancy tests include checking for levels of early pregnancy factor (EPF) or performing an ultrasound. EPF can be detected 48 hours after fertilization, but because of its high expense, the test is rarely used unless there is an urgent medical need to establish whether a woman is newly pregnant. Ultrasounds are seldom used for pregnancy tests because they are less sensitive than early blood and urine tests.
Types of Pregnancy Tests
Human chorionic gonadotropin can be detected in the bloodstream and urine of a pregnant woman. Home pregnancy tests are made to test urine, while a doctor's pregnancy test may examine either urine or blood samples.
Blood tests are generally more sensitive than urine tests. There is also a range of effectiveness for home pregnancy tests, with some more accurate than others. Most home tests can accurately detect a pregnancy around the time that a woman's period is expected, or two weeks after she ovulates.
Accuracy of Home Pregnancy Tests
Home pregnancy tests are very accurate after a certain point in the pregnancy. False negatives are very common in early pregnancy, because the tests can't detect a fertilized embryo that hasn't yet implanted in the uterus, and they may not be sensitive enough to detect the low levels of hCG present in even the first few days after implantation.
Once a menstrual period is late, the accuracy of home tests rises markedly as long as they are being used correctly. However, home pregnancy tests with lower sensitivity to hCG may give a false negative as much as three weeks after conception.
It's also possible for tests used inaccurately or past their expiry date to result false positives. Other false positives can occur if a woman is taking fertility treatments that include hCG, or due to certain liver diseases, cancers and other medical problems. Regardless of the result produced by a home pregnancy test, it's always a good idea to see a doctor if pregnancy is suspected, especially if the patient is experiencing such common signs as fatigue, nausea, backaches, headaches, cramping and breast changes. A family doctor can order a blood or urine test to establish whether or not the patient is pregnant.
What to Expect in a Pregnancy Test
Pregnancy tests are simple, painless and completely risk-free:
- Medical pregnancy tests require blood to be drawn for lab analysis, or a urine sample to be collected.
- Home pregnancy tests are generally of the "pee on the stick" variety, where a urine sample must be applied to a sensor mechanism on the test kit. Within minutes, the test will indicate a positive or negative result.
Results of the Pregnancy Test
The results of a home pregnancy test can have a dramatic effect on the rest of one’s life. Whatever the results, it's a good idea to get a second opinion in the form of another home test or a blood test ordered by a doctor.
If tests show pregnancy, a woman should always consult your family doctor or a reproductive health clinic for advice and care. Until a doctor can confirm a pregnancy, it's important for women to eat well and avoid alcohol, caffeine, tobacco, and other drugs or chemicals that might harm a developing baby.
Are you in need of a pregnancy test? Please consult our Pregnancy Test Directory. To learn more about pregnancy tests, read our interview with Mollee Bloom Bauer, pregnancy test expert.