Human Chorionic Gonadotrophin (hCG)

Most commercially available monoclonal antibody-based urine pregnancy tests can detect the presence of human chorionic gonadotrophin (hCG) at a level above 25 IU/L, which corresponds to day 24–25 of a regular 28-day cycle. In normal early pregnancies, serum hCG levels double approximately every 2 days. In clinical practice, the measurement of serum hCG is used to diagnose ectopic pregnancy; to help select patients for expectant, medical and surgical management of early pregnancy failure; and to assess the efficacy of treatment at follow-up visits.

Traditionally, an ectopic pregnancy is suspected in women in whom intrauterine pregnancy is not demonstrated on ultrasound. In this situation, many clinicians resort to the assessment of the daily rate of serum hCG levels. An ectopic pregnancy is suspected if the hCG does not double in 2–3 days. Another approach to the diagnosis of ectopic pregnancy is to use a cut-off level above which an intrauterine pregnancy should be seen on ultrasound. With the use of transvaginal sonography this level has been set to the serum hCG level of 1000 IU/L (the first International Standard). However, neither abnormal doubling time nor the cut-off method is sensitive or specific enough to diagnose ectopic pregnancy.

Serum hCG measurement is also used for selection of women for conservative or medical management of ectopic pregnancy. Expectant management of ectopic pregnancy is likely to be successful if the initial hCG is < 1000 IU/L and medical treatment of tubal ectopic is rarely used if the hCG > 15 000 IU/L because the risk of failure and complications is increased.