BETA HCG

Clinical Significance:

HCG stands for Human chorionic gonadotropin. HCG is a glycoprotein with a molecular weight of 50,000 daltons. Each molecule consists of an alpha subunit of 18,000 daltons and a beta subunit of 32,000 daltons. This hormone’s function includes facilitation of implantation as well as maintenance and development of the corpus luteum. Pregnancy tests are based on the detection of the hormone HCG in urine or serum. HCG is thought to be produced by trophoblastic tissue and it appears around the 8-9th day after ovulation where fertilization has occurred, or around the 4th day after conception.

In a 28-day cycle with ovulation occurring at day 14, HCG can be detected in urine or serum in minute quantities around day 23, or 5 days before the expected menstruation. Human chorionic gonadotrophin circulates as the intact molecule in the serum of women who have an uncomplicated pregnancy. The relative concentrations of intact and subunit HCG in serum and urine vary a great deal in patients with trophoblastic disease because of unbalanced synthesis of subunits. Chorionic gonadotrophin assays are sometimes used to support the diagnosis of ectopic pregnancy. Ectopic gestations do not develop or secrete HCG as do intrauterine pregnancies.
Twin pregnancies tend to show higher HCG levels on a given day of pregnancy. However, there is a large variation in HCG levels between pregnancies, and much overlap exists between single and twin pregnancies.

There are three points during pregnancy when the levels of B-hCG present in the blood become important.The first is the one mentioned before, namely when the level rises enough to produce a positive pregnancy test. (Note: Even though a positive urine based test is often the basis on which you contact your doctor, he/she will almost certainly ask you to perform a blood analysis to obtain a more accurate confirmation of the levels).The second point during pregnancy where in B-hCG values are important is to notice the doubling of the ß-hCG values in 48 hours . This serves for confirming that growth of the baby is proper in initial stages.

The third time during pregnancy that the levels of ß-hCG are important is during the screening test called the “Triple Test”. This test is also referred to as “The Multiple Marker Test” and “The AFP-Plus Test”. During, this test, a blood sample is taken and tested for three specific proteins, one of which is HCG, (There is a debate as to whether HCG or free beta-HCG is the best method). The combination of measurements combined with information about the mother can indicate either Spina-Bifida or Down Syndrome. The levels of ß-hCG should drop away 8-9 weeks into the pregnancy (as the placenta takes over production of progesterone), if higher than expected levels of ß-hCG are found between 15 and 22 weeks, then this could indicate an abnormal foetus development.