Human chorionic gonadotropin (hCG) hormone is secreted by the placenta after insemination. hCG can be defected in human urine (and also in blood or serum) at least 5-15 days after the pregnancy has started. The hCG level in the urine/serum after the first missed period is generally around 100mlU/ml and in the first three months the hCG levels rise and reach 100,000-200,000 mlU/ml.
Easy detection of hCG in urine and serum right after insemination and rapidly rising levels in the early stages of pregnancy make this hormone a reliable and good detection material for early diagnosis of pregnancy. The aim of this test is to detect early beta hCG development that is above 20mlU/ml.
In normal pregnancy, hCG can be detected 7-10 days after conception. Usually, the test can be used as early as the first day of a missed period. If the menstrual cycle length is irregular, the test time can be based on the longest cycle length that occurred in the past few months. If a negative result is obtained and pregnancy is still suspected, the test can be repeated in 2-4 days. In normal pregnancies hCG will reach 20 iu/L in 4-5 days (visible as a weak positive). However the detection of hCG at this level does not necessarily indicate a viable pregnancy as implantations can spontaneously abort.
An ectopic pregnancy will show a much slower rise or even plateau with hCG values lower than for a comparable stage of normal pregnancy. A fall in concentration will suggest a failing pregnancy or miscarriage. The time post miscarriage before the levels become undetectable will depend on the peak level of hCG reached.
Raised levels of hCG are also present in other conditions e.g. hydatidiform moles/choriocarcinoma.