How does hcg work

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 8, 2026

Quick Answer: Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy that maintains progesterone production by the corpus luteum until the placenta takes over around 8-10 weeks gestation. Structurally, hCG is a glycoprotein composed of 237 amino acids with a molecular weight of approximately 36.7 kDa, consisting of alpha and beta subunits. It functions by binding to luteinizing hormone (LH) receptors on ovarian cells, stimulating progesterone synthesis crucial for maintaining the uterine lining. Beyond pregnancy, hCG is used medically for fertility treatments to trigger ovulation and in weight loss programs, though the latter application is controversial and not FDA-approved.

Key Facts

hCG is produced by the syncytiotrophoblast cells of the placenta, with levels detectable in blood as early as 7-10 days after conception
During early pregnancy, hCG levels typically double every 48-72 hours, peaking at 8-11 weeks at approximately 100,000 mIU/mL
The beta subunit of hCG is unique and forms the basis for pregnancy tests, with most home tests detecting levels as low as 25 mIU/mL
In fertility treatments, hCG injections of 5,000-10,000 IU are commonly administered to trigger final oocyte maturation
The controversial hCG diet protocol involves daily injections of 125-200 IU combined with a 500-calorie diet, though multiple studies show weight loss results from caloric restriction alone

Overview

Human chorionic gonadotropin (hCG) is a glycoprotein hormone first discovered in 1927 by German scientists Selmar Aschheim and Bernhard Zondek, who identified it as the substance responsible for the positive pregnancy test in rabbits. Produced primarily by the syncytiotrophoblast cells of the placenta during pregnancy, hCG plays a crucial role in early gestation. The hormone's name derives from its origin (chorionic) and its effect on the gonads. Structurally, hCG consists of 237 amino acids arranged in two subunits: an alpha subunit identical to those of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH), and a unique beta subunit that gives hCG its specific biological activity. This structural similarity to LH allows hCG to bind to LH receptors, explaining its physiological effects. Beyond its natural role in pregnancy, hCG has found applications in reproductive medicine since the 1960s and has been marketed for weight loss since the 1950s, though the latter use remains scientifically controversial.

How It Works

hCG functions through a precise molecular mechanism beginning with its binding to luteinizing hormone (LH) receptors on the corpus luteum in the ovary. This binding activates adenylate cyclase, increasing intracellular cyclic AMP (cAMP) levels, which in turn stimulates the production of progesterone. Progesterone is essential for maintaining the endometrial lining of the uterus, preventing menstruation, and supporting early pregnancy. During the first 8-10 weeks of gestation, hCG sustains the corpus luteum's progesterone production until the placenta becomes capable of producing sufficient progesterone independently. The hormone also promotes angiogenesis (blood vessel formation) in the uterine vasculature and has immunomodulatory properties that may help prevent maternal rejection of the developing embryo. In fertility treatments, exogenous hCG mimics the natural LH surge, triggering final oocyte maturation and ovulation approximately 36-40 hours after administration. The hormone's half-life of approximately 24-36 hours (compared to LH's 20-minute half-life) makes it particularly effective for this purpose.

Why It Matters

hCG's significance extends across multiple domains of human health and medicine. In obstetrics, it serves as the earliest biochemical marker of pregnancy, with home pregnancy tests detecting hCG in urine with over 99% accuracy when used correctly after a missed period. Abnormal hCG patterns can indicate ectopic pregnancies, miscarriages, or gestational trophoblastic diseases like molar pregnancies. In reproductive medicine, hCG injections are standard in assisted reproductive technologies (ART), with approximately 1.9% of all U.S. infants born in 2021 conceived using ART procedures often involving hCG. The hormone's controversial use in weight loss programs, while popularized by British endocrinologist Albert T.W. Simeons in the 1950s, has been repeatedly challenged by scientific evidence; the FDA has required hCG products marketed for weight loss to carry warnings since 1975. Research continues into hCG's potential therapeutic applications, including its possible neuroprotective effects and role in cancer treatments, particularly for testicular and ovarian cancers where hCG receptors may be overexpressed.