Human Chronic Gonadotropin (HCG) has proved to be an amazing molecule. It was introduced as a hormone with endocrinal bearings. However, recent reports have completely changed the understanding of this molecule and opened new areas of application. No wonder, obstetricians require to take a new look at it.


HCG is detected both in urine and in serum. With modern methods of detection being very sensitive, the correlation between serum & urinary levels is very consistent. As a result, it matters little which one is assayed for clinical application. However, serum HCG is most popularly assayed now.

HCG has an endocrinal half-life of maximum 72 hours. However, HCG half-life as a hormone has much farther bearing that will be understood in the paragraphs to follow.

HCG levels are at its peak on 70th day of pregnancy and plateau by 100th day of pregnancy. This is exactly congruent with the behavior of emesis gravidarum. Vomiting of pregnancy is also at its peak at around 70th day and plateaus by 100th day.


It may seen strange but is indeed true that it is HCG which informs the mother that she has conceived. Thus HCG is secreted by the blastocyst itself and by the time the chorionic tissue takes over, HCG is already old in the mother. This HCG secretion is required by the mother to tolerate the pregnancy immunologicaly. Mother at her decidual-placental interface mounts a complex but intricate protective response so as to protect the conceptus. The conceptus is immunologicaly similar to the mother but is distinct due to paternal contribution. This can endanger every conceptus. On sensing that a conceptus is within her, thanks to HCG, the mother starts protecting it.


A conceptus is indeed a male or a female due to its basic chromosomal structure - XX or XY. However, this chromosomal structure has to affect a series of changes in the conceptus so that the fetus is either a male or a female. Interestingly an essential agent that helps the genetic expression of this sex structure of the conceptus is HCG. It acts on the adrenal and ovarian tissues to bring about a differentiation into a male or a female.


Various articles and work done by many groups showed a distinct role of HCG supplement in preventing recurrent pregnancy loss. In some of these studies it was found that HCG if given weekly, also showed its results. This created an enigma. On one side we have a short half life of HCG tittering around 72 hours. On the other had one was getting good results with HCG being supplemented at a weekly interval. If was soon obvious that there was much more to HCG than merely a hormone.

Soon studies got published showing a contamination of HCG with, growth factors. It was thence explained that it was this contamination which resulted in protecting the pregnancy much beyond the endocrinal half-life. Soon further interesting results emerged. One of these showed that HCG has a very similar structure to growth factors. Studies in late 1997 and 1998 in fact showed that HCG itself was the growth factor. Once HCG is proved to be the growth factor, it is very clear that when in a given clinical situation, HCG is administered, one is not giving an endocrinal substance but an immunological substance.

To what extent is this similar to the LH is being currently investigated. LH is now proved to have both endocrinal LH component and an immunoreactive LH component. Whether, this is true for HCG as well, is a matter being investigated. All in all, the clinical discovery of such an investigation gives the explanation to the affectivity of HCG even when administered at a seven days interval.


Nowhere has the face of an obstetric condition changed as has been in ectopic pregnancy. This has been largely due to HCG and Trans Vaginal Sonography (TVS). Doubling time was a singular parameter used clinically wherein an early diagnosis of ectopic pregnancy became possible. It was found that in an intra uterine pregnancy, HCG levels double every 48 hours. However, if by 48 hours HCG levels increase by less than 66% one should strongly suspect an ectopic pregnancy.

However, when HCG is combined with ultra sonography very early diagnosis of an ectopic pregnancy became easy. It is now well established that in a given case if HCG levels are greater than 1500 miu/ml and one fails to visualize an intrauterine gestation, ectopic pregnancy is one the cards. On other hand if a Trans Abdominal Sonography (TAS) does not show an intrauterine pregnancy at or above 6500 miu/ml of HCG – an ectopic pregnancy is on the cards.

Modern management of ectopic pregnancy includes medical and expectant. In a given case if the G.S. is less than 2.5 cms in size, fetal pole does not show cardiac activity and free blood is less than 50 ml., medical treatment can be given. 75 mgms. of methotrexate is preferred by us and monitoring with 12 hourly USG and 48 hrs. HCG be done. Soon HCG start falling indicating the response is said to have achieved. Even in expectant management, when methotrexate is not given and spontaneous resolution is expected HCG and TVS are the mainstays in their treatment.


HCG as a part of triple test in combination with urinary estriol (UE3) and serum alpha feto protein can reasonably accurately diagnose a trisomy 21 (T21). It has been found that maternal age greater than 35, low UE3 High serum HCG and low serum <AFP can give a diagnosis of T21 with a near 96% accuracy. Similar combinations have been worked out for T18, anencephaly etc.


With the immunological role of HCG now well defined it is understandable that HCG may be employed to pick up PIH. HCG estimated at 15 weeks can predict a PIH with reasonable accuracy. Studies are currently on to understand this aspect of HCG before it is established.


Use of HCG in cases of trophoblastic diseases and ovulation induction is well known. This can span the span of entire articles and are therefore just mentioned to complete the list. 



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