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The Test Sample
What is being tested?
Human chorionic gonadotropin (hCG) is a hormone produced by the placenta of a pregnant woman. Early in pregnancy, the level of hCG increases in the blood and is eliminated in the urine. A pregnancy test detects hCG in the blood or urine and confirms or rules out pregnancy.
During the early weeks of pregnancy, hCG is important in maintaining function of the corpus luteum. Production of hCG increases steadily during the first trimester (8-10 weeks) of a normal pregnancy, peaking around the 10th week after the last menstrual cycle. Levels then fall slowly during the remainder of the pregnancy. hCG is no longer detectable within a few weeks after delivery.
When a pregnancy occurs outside of the uterus (ectopic), the level of hCG in the blood increases at a slower rate. When an ectopic pregnancy is suspected, measuring the level of hCG in the blood (quantitative test) over time may be useful in helping to make a diagnosis of ectopic pregnancy.
Similarly, the hCG blood level may be abnormal when the developing baby (fetus) has a chromosome defect such as Down syndrome. An hCG test is used routinely in conjunction with a few other tests as part of screening for fetal abnormalities. (See First Trimester Down Syndrome Screen or Second Trimester Maternal Serum Screening for more on this.)
How is the sample collected for testing?
Preferably, a urine sample is collected first thing in the morning or a blood sample is drawn from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed. However, do not drink large amounts of fluid before collecting a urine sample for a pregnancy test. This is because overly dilute urine may result in a false negative.