Chorionic gonadotropin, usually called hCG (human chorionic gonadotropin), is a hormone produced during pregnancy that keeps the early embryo alive by signaling the body to maintain its supply of progesterone. It’s the hormone detected by every pregnancy test on the market, and it also has medical uses in fertility treatment for both women and men. Outside of pregnancy, abnormal hCG levels can signal certain cancers, making it a valuable diagnostic tool as well.
How hCG Works in Early Pregnancy
After a fertilized egg implants in the uterine wall, cells that will eventually become the placenta begin producing hCG almost immediately. The hormone’s primary job is to keep the corpus luteum, a temporary structure on the ovary, alive and functioning. The corpus luteum produces progesterone, which thickens the uterine lining and prevents menstrual bleeding. Without hCG sending that signal, progesterone levels would drop and the pregnancy would end.
This role is critical but surprisingly brief. hCG only needs to support the corpus luteum for about 3 to 4 weeks after implantation, roughly the first 10% of pregnancy. After that, the placenta itself takes over progesterone production and the corpus luteum is no longer essential.
hCG Levels Through Early Pregnancy
In a healthy pregnancy, hCG levels rise rapidly and follow a fairly predictable pattern, though individual variation is wide. At 4 weeks of pregnancy (around the time of a missed period), blood levels typically range from 0 to 750 µ/L. By week 5, they climb to 200 to 7,000 µ/L. At 6 weeks the range broadens to 200 to 32,000 µ/L, and by week 7 levels can reach 3,000 to 160,000 µ/L. The peak arrives between weeks 8 and 12, when levels can hit 32,000 to 210,000 µ/L before gradually declining for the rest of the pregnancy.
Doctors sometimes track hCG levels through repeated blood draws in early pregnancy. A number that doubles roughly every 48 to 72 hours is generally reassuring. Levels that rise too slowly can suggest a potential miscarriage or ectopic pregnancy, while unusually high levels may indicate a multiple pregnancy or, rarely, a problem with the placental tissue itself.
Why hCG Matters Beyond Pregnancy Tests
hCG acts on the same receptor as luteinizing hormone (LH), one of the key hormones that controls reproductive function in both sexes. Research shows hCG is actually about 10 times more potent than LH at triggering the cellular signaling cascade that leads to hormone production. This potency is what makes it so useful as a medication.
In men, hCG stimulates the same testicular cells that LH normally targets, prompting them to produce testosterone. The end result is the same, with both hormones driving testosterone production in a dose-dependent way. This shared biology is the basis for most of hCG’s medical applications outside of pregnancy.
Medical Uses in Fertility Treatment
The FDA has approved prescription hCG for treating female infertility, where it’s used to trigger ovulation. Because hCG mimics the natural LH surge that causes an egg to release from the ovary, a precisely timed injection can help coordinate egg retrieval during IVF or improve the chances of conception during other fertility procedures.
In men, hCG has several important fertility applications. Men on testosterone replacement therapy often experience a drop in sperm production because the external testosterone signals the brain to stop producing LH, which the testes need to make sperm. Adding hCG to a testosterone regimen can preserve sperm production by maintaining testosterone levels inside the testes. For men who want to conceive within six months, the typical approach involves stopping testosterone therapy and switching to hCG alone to restart natural sperm production.
Men with a condition called hypogonadotropic hypogonadism, where the brain doesn’t send enough hormonal signals to the testes, can use hCG to directly stimulate testosterone production. If sperm production doesn’t resume within four to six months on hCG alone, additional hormonal support is often added. hCG-based treatments have also been used to help men recover sperm production after long-term anabolic steroid use, though the process can take months.
hCG as a Cancer Marker
Certain cancers produce hCG, which makes a blood test for the hormone useful in diagnosis and monitoring. Testicular germ cell tumors are the most well-known example. hCG levels, along with two other blood markers, play a direct role in diagnosis, staging, risk classification, and treatment planning for these cancers. Some types of testicular cancer raise hCG levels consistently, while others do so only occasionally.
Gestational trophoblastic disease, a group of rare conditions involving abnormal growth of placental tissue, also produces hCG. In these cases, tracking hCG levels over time helps doctors determine whether treatment is working or whether the disease has returned. Because the body normally produces no significant hCG outside of pregnancy, even a small elevation in a non-pregnant person is a meaningful finding.
The Hook Effect: When Tests Give Wrong Answers
In rare cases, extremely high hCG levels can actually cause a pregnancy test to show a false negative. This phenomenon, called the hook effect, happens because home pregnancy tests work by using antibodies that bind to hCG molecules in a specific sandwich-like arrangement. When hCG levels are extraordinarily high, the massive excess of hormone overwhelms the limited antibodies on the test strip, preventing them from forming the correct complex. The result is a negative reading despite an obvious pregnancy.
This is most likely to occur later in pregnancy when hCG is at its highest, or in cases of gestational trophoblastic disease where levels are abnormally elevated. A simple fix is diluting the urine sample before retesting, which reduces the hCG concentration enough for the test to work properly. Blood tests ordered by a doctor are far less susceptible to this problem.
hCG and Weight Loss: A Debunked Claim
Over-the-counter hCG products marketed for weight loss are sold as drops, pellets, and sprays, often paired with an extremely restrictive 500-calorie-per-day diet. The FDA has been clear: hCG is not approved for weight loss, and there is no substantial evidence that it increases weight loss beyond what the severe calorie restriction alone would cause. The prescription drug label itself states that hCG does not reduce hunger, redistribute fat, or improve results compared to dieting alone.
The real danger lies in the diet that accompanies these products. Eating only 500 calories a day puts people at risk for gallstones, dangerous electrolyte imbalances that affect heart and muscle function, and irregular heartbeat. The FDA advises consumers to avoid all hCG weight-loss products and notes that hCG is not approved for any over-the-counter use.