How can blood pregnancy tests (hCG tests) be used to check the length of pregnancy or the success of an abortion?

Human chorionic gonatropin (hCG), often called the “pregnancy hormone”, is a hormone that body produces in large quantities during the beginning of pregnancy. Testing for this hormone is common way of confirming a pregnancy. Widely available urine pregnancy tests can usually detect this hormone once the period is late.

HCG blood tests can either be qualitative (+ or -) or quantitative. Qualitative tests will only say whether there is an elevated amount of hCG in the blood or not. Quantitative tests give the specific amount of hormone in the blood. This number can give a broad indication of the length of pregnancy, or it can help to determine if a pregnancy is continuing.

If the level is lower than 5 mIU/mL – there is no pregnancy. If the test is taken to see how long the pregnancy is, the amount of hormone in the blood can give a very rough estimation of the pregnancy length. If the test is being used to determine if a pregnancy is continuing (for example after an abortion or possible miscarriage), two tests need to be taken with about 2-4 days in between. If the levels rise, it means pregnancy is developing, if it drops it means the pregnancy stopped.

The blood tests are reliable in indicating whether the pregnancy is developing or stopped until about 10 weeks of pregnancy. After about 10 weeks, the hCG level drops and becomes stable afterwards.