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Pregnancy & Prenatal Testing

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First Trimester: Pregnancy Test

If pregnancy is only suspected, or if the pregnancy test was not performed through the health care provider (such as an at-home urine pregnancy test), then a pregnancy test may be requested to confirm that a woman is pregnant.

Pregnancy tests all measure the same substance, human chorionic gonadotropin (hCG), a hormone that is produced by the placenta when a woman is pregnant. The amount of hCG produced during pregnancy doubles every two to three days and then levels off in the second or third month of pregnancy. Qualitative urine and blood pregnancy tests can detect hCG as early as several days to two weeks after conception.

Quantitative blood pregnancy testing measures the actual amount of hCG present. Each woman will produce the hormone at a slightly different rate, but women with normal pregnancies should have hCG concentrations that fall within established ranges for each week of gestation. Quantitative hCG tests may be repeated every couple of days if there is a problem with the pregnancy to look at changes in the concentration of hCG.

A level of hCG lower than expected may be due to incorrect calculation of gestational age or a problem in fetal development, which may lead to miscarriage. The test may be repeated or an ultrasound done to compare the size of the developing baby to the expected size for the duration of pregnancy. Patients with ectopic pregnancies will have lower than expected values that will increase more slowly than expected. Patients who have failing pregnancies may have stagnant or dropping hCG levels.