Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy that keeps the early pregnancy viable by signaling the body to maintain progesterone production. But hCG plays roles well beyond pregnancy: it’s the hormone detected by pregnancy tests, it’s used in fertility treatments, it serves as a cancer marker, and it can stimulate testosterone production in men. Here’s how it works in each of those contexts.
How hCG Sustains Early Pregnancy
After a fertilized egg implants in the uterine wall, the developing placenta begins releasing hCG into the bloodstream. The hormone’s primary job is to keep the corpus luteum alive. The corpus luteum is a temporary structure in the ovary that forms after ovulation, and it produces progesterone, the hormone that thickens the uterine lining and prevents menstrual bleeding. Without hCG, the corpus luteum would break down within about two weeks, progesterone would drop, and the uterine lining would shed, ending the pregnancy before it could take hold.
This rescue mission lasts roughly 3 to 4 weeks after implantation, covering about 10% of the total pregnancy. After that window, the placenta itself takes over progesterone production and the corpus luteum is no longer needed. hCG levels reflect this transition: they rise rapidly in the first trimester, peak around weeks 9 to 10 (with a median near 75,000 mIU/mL), then gradually decline through the rest of pregnancy.
hCG Levels and Doubling Time
In early pregnancy, hCG levels roughly double every 1.4 to 3.5 days. That doubling time isn’t constant. It slows as levels climb and gestational age increases. Doctors sometimes track this doubling pattern with serial blood draws to assess whether a pregnancy is progressing normally. A significantly slower rise can signal a potential problem like an ectopic pregnancy or miscarriage, while an unusually rapid rise may suggest a molar pregnancy or twins.
To give a sense of the range, here’s what typical hCG levels look like across the first trimester:
- Before week 9: Median around 60,000 mIU/mL, but anywhere from about 2,300 to 94,000 falls within the normal range
- Weeks 9 to 10: Median around 75,000 mIU/mL, ranging from roughly 24,000 to 138,000
- Week 12: Median drops to about 56,000 mIU/mL as the placenta takes over
These ranges are wide, so a single hCG number on its own rarely tells the full story. The trend over multiple measurements matters more than any individual reading.
Why Pregnancy Tests Detect hCG
Home pregnancy tests work by detecting hCG in urine. The hormone appears in blood and urine only when a pregnancy (or certain medical conditions) is producing it, making it a reliable marker. Most standard home tests can detect hCG at concentrations of about 22 mIU/mL. Early-detection tests, like First Response, are sensitive down to about 5.5 mIU/mL, which is why they can sometimes pick up a pregnancy a few days before a missed period. Blood tests ordered by a doctor are even more sensitive and can detect hCG at very low concentrations, which is useful for monitoring early or high-risk pregnancies.
hCG in Fertility Treatments
Because hCG acts on the same receptor as luteinizing hormone (LH), the natural hormone that triggers ovulation, doctors use hCG injections as a “trigger shot” in fertility treatments. After a woman’s follicles have been stimulated to grow with other medications, a single hCG injection mimics the LH surge that would naturally cause the egg to mature and release. Ovulation typically occurs 36 to 48 hours after the injection, allowing doctors to precisely time procedures like intrauterine insemination or egg retrieval for IVF.
hCG has a longer half-life than LH, which means it stays active in the body longer and provides a more sustained signal. This makes it practical for clinical use, since a single injection can do the work that the body’s natural LH surge accomplishes over a shorter window.
How hCG Works in Men
Men don’t produce hCG naturally in significant amounts, but the hormone has a clear biological effect when administered. Because it mimics LH, hCG stimulates Leydig cells in the testes to produce testosterone. This makes it useful for treating certain forms of low testosterone, particularly when preserving fertility matters. Standard testosterone replacement therapy shuts down the body’s own signals to the testes, which can shrink them and reduce sperm production. hCG, by contrast, stimulates the testes directly, maintaining both testosterone output and testicular function.
hCG as a Cancer Marker
Outside of pregnancy, elevated hCG in the blood can be a sign of certain cancers. In testicular cancer, tumor cells can transform into a type of cell normally found in the placenta and begin secreting hCG. Normal levels in a non-pregnant person are below 5 IU/L. Levels above 5,000 IU/L in testicular cancer typically indicate a more aggressive form of the disease. hCG can also be elevated in cancers of the liver, lung, pancreas, and stomach, making it a useful (though not definitive) tool for diagnosis and for tracking whether treatment is working. After surgery or chemotherapy, doctors monitor hCG levels to watch for recurrence.
The hCG Weight Loss Diet Is Not Supported
hCG has been marketed as a weight loss aid, typically as drops or injections paired with an extremely low-calorie diet of around 500 calories per day. The FDA has explicitly warned consumers to avoid these products. The agency’s position is clear: there is no substantial evidence that hCG increases weight loss beyond what comes from severe calorie restriction alone, and it does not cause a more favorable distribution of body fat or reduce hunger.
The weight loss people experience on these programs comes entirely from eating 500 calories a day, which is itself dangerous. That level of calorie restriction increases the risk of gallstones, electrolyte imbalances that can disrupt heart rhythm and muscle function, and irregular heartbeat. The FDA has approved hCG only as a prescription drug for female infertility and specific medical conditions. It is not approved for weight loss, and over-the-counter hCG products sold for this purpose are considered illegal by the FDA.