Back Blood-tests Explained


Pregnancy Test


At a Glance

Why Get Tested?

To confirm a pregnancy; to help identify an ectopic pregnancy; to monitor a pregnancy that may be at risk of failing; occasionally to screen a woman for pregnancy prior to some medical treatments; as part of a panel of tests used to screen for fetal abnormalities (see First Trimester Down Syndrome Screen and Second Trimester Maternal Serum Screening)

When to Get Tested?

When you suspect that you are pregnant (testing can be done reliably by 10 days after you miss your menstrual period and some methods can detect hCG even earlier); when you have signs and symptoms that suggest you may have an ectopic pregnancy or a pregnancy that is failing; prior to some medical treatments

Sample Required?

A urine sample collected first thing in the morning or a blood sample drawn from a vein in your arm

Test Preparation Needed?

Do not drink large amounts of fluid before collecting a urine sample for a pregnancy test because overly diluted urine may result in a false negative; no preparation is needed for a blood sample.

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.

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.

The Test



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