Human chorionic gonadotropin (HCG) is a hormone produced by the placenta during pregnancy. This hormone plays an important role in maintaining the survival of the early embryo by stimulating the ovaries to produce hormones like progesterone and estrogen. In this article, we will discuss the key functions of HCG along with some medical uses and controversies surrounding this hormone.

What is HCG?

Human chorionic gonadotropin, commonly referred to as HCG, is a hormone produced by cells that form the placenta, which connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. Specifically, HCG is produced by trophoblast cells, which surround the embryo during early pregnancy. It consists of 237 amino acids and belongs to a family of hormones known as glycoprotein hormones.

HCG starts to be produced as soon as the embryo implants into the uterine wall, with levels rising steadily during the first trimester and peaking around the 10th week of gestation before declining. HCG levels in the mother's blood and urine are routinely tested during early pregnancy to confirm pregnancy and later to determine fetal development stage.

Functions of HCG

The primary functions of HCG in early pregnancy are:

- Preventing luteolysis: HCG acts on the ovaries to maintain the corpus luteum, which produces progesterone. Progesterone is needed to sustain the thickening of the uterine lining to support the developing embryo.

- Promoting steroidogenesis: HCG stimulates the production of estrogen and progesterone by the ovaries. These hormones are essential for the proper development of the embryo and maintenance of pregnancy.

- Contributing to placental development: HCG induces angiogenesis (formation of new blood vessels) and stimulates the growth of the placenta.

- Aiding embryo implantation and development: Studies suggest HCG may have a direct effect on the embryo by promoting cell division and growth during the critical early stages after implantation.

Medical Uses of HCG

Some clinical applications of HCG outside of pregnancy include:

- Infertility treatment: HCG injections can induce ovulation in women and stimulate the maturation of testicular eggs called spermatozoa in men. It is commonly used along with fertility drugs.

- Weight loss: When combined with a very low-calorie diet, HCG injections are claimed to promote fat loss, particularly from problem areas like the abdomen. However, this usage remains controversial.

- Turner syndrome: HCG injections can stimulate sexual maturation in young girls with Turner syndrome lacking complete sexual development due to Turner syndrome.

- Undescended testes: In infants, HCG injections are sometimes used to help naturally undescended testes move into the scrotum in a non-surgical procedure called orchidopexy.

Controversies around HCG Use

While HCG is well established for infertility and pregnancy uses, some applications like weight loss remain questionable:

- Most weight loss studies using HCG are poorly designed with small sample sizes, no controls, and short follow-up periods. Mechanism of action is unclear.

- Larger, better controlled trials have found no significant long-term effects on weight loss compared to low-calorie diets alone. Effects seen may be due to diet or placebo effect alone.

- There are safety concerns with off-label HCG injections which bypass normal physiological regulation and produce supraphysiological hormone levels of unknown consequences.

- Underground hGH markets notoriously sell unregulated versions of HCG for weight loss which may contain other unlabeled compounds or dosages.

In conclusion, more research is still needed to validate weight loss and other non-pregnancy applications of HCG. For now, pregnancy-related uses per doctor guidance are considered the only evidence-based functions.