Human chorionic gonadotropin, or hCG, is a hormone produced during pregnancy that signals the body to maintain the conditions needed to support a developing embryo. It’s the hormone that pregnancy tests detect, and it plays a central role in early pregnancy by keeping progesterone levels high enough to sustain the uterine lining. Outside of pregnancy, hCG also serves as a medical treatment for certain fertility problems and as a diagnostic marker for specific cancers.
How hCG Works in Early Pregnancy
After a fertilized egg implants in the uterus, the outer layer of the developing embryo (called the chorion) begins producing hCG. The hormone’s primary job is to rescue a small structure on the ovary called the corpus luteum, which forms after ovulation. Without pregnancy, the corpus luteum breaks down within about two weeks. hCG keeps it alive and functioning, which is critical because the corpus luteum produces progesterone, the hormone that maintains the uterine lining where the embryo has implanted.
hCG does this by binding to the same receptors that luteinizing hormone (LH) uses, essentially mimicking LH’s signal but sustaining it for weeks longer than a normal menstrual cycle would allow. This triggers cells in the corpus luteum to ramp up production of the enzymes responsible for making progesterone. The corpus luteum continues this role until roughly weeks 8 to 12, when the placenta takes over progesterone production on its own.
Structurally, hCG is a glycoprotein made of two linked pieces: an alpha subunit that it shares with several other hormones (including LH, FSH, and thyroid-stimulating hormone) and a unique beta subunit. Pregnancy tests specifically target that beta subunit to avoid confusing hCG with those related hormones.
How hCG Levels Change Week by Week
hCG rises rapidly in early pregnancy, typically doubling every 48 to 72 hours during the first several weeks. The wide ranges at each stage reflect normal variation between pregnancies:
- 4 weeks: 0 to 750 µ/L
- 5 weeks: 200 to 7,000 µ/L
- 6 weeks: 200 to 32,000 µ/L
- 7 weeks: 3,000 to 160,000 µ/L
- 8 to 12 weeks: 32,000 to 210,000 µ/L
Levels peak somewhere between weeks 8 and 12, then gradually decline and plateau for the remainder of pregnancy. A single hCG reading matters less than the pattern over time. Levels that fail to rise appropriately can signal a problem like an ectopic pregnancy, while unusually high levels may point to a molar pregnancy, a rare condition where abnormal placental tissue grows instead of a normal embryo. In one study, hCG levels above 126,278 mIU/mL at 10 to 11 weeks were most commonly associated with complete molar pregnancies, while levels below 30,000 mIU/mL at the same stage pointed toward ordinary miscarriage.
When Pregnancy Tests Can Detect hCG
If you have a typical 28-day menstrual cycle, hCG becomes detectable in urine about 12 to 15 days after ovulation, which lines up roughly with the day of your expected period. Blood tests can pick up hCG slightly earlier because they measure lower concentrations, though the exact advantage varies.
Not all home pregnancy tests are equally sensitive. A study comparing over-the-counter tests found dramatic differences. First Response Early Result detected hCG at concentrations as low as 6.3 mIU/mL, catching over 95% of pregnancies by the day of the missed period. Clearblue Easy Earliest Results required 25 mIU/mL, detecting about 80% of pregnancies at that point. Five other products needed 100 mIU/mL or more, catching only 16% or fewer pregnancies on the first day of a missed period. If you’re testing early, the brand and sensitivity threshold on the box make a real difference.
hCG in Male Fertility and Hormone Therapy
Because hCG mimics LH, it can stimulate the testes to produce testosterone and support sperm production. This makes it a useful treatment for men with certain types of low testosterone, particularly hypogonadotropic hypogonadism, a condition where the brain doesn’t send enough hormonal signals to the testes.
Men on testosterone replacement therapy face a common problem: external testosterone suppresses the body’s own production, which can shrink the testes and halt sperm production. hCG injections help counteract both of these effects by maintaining the internal testosterone signal within the testes. For men who want to preserve fertility while treating low testosterone, hCG can be cycled alongside or in place of testosterone therapy.
hCG also plays a role in recovery for men who have used anabolic steroids. Long-term steroid use can shut down the body’s natural testosterone production. Treatment protocols typically start with hCG alone for three to six months to restart testicular function, adding additional hormonal support only if sperm production doesn’t resume on its own.
hCG as a Cancer Marker
Outside of pregnancy and fertility treatment, elevated hCG in the blood can be a warning sign for certain cancers. Testicular cancer is the most well-known example. In germ cell tumors of the testes, cancerous cells can transform into a type of cell normally found in the placenta, which then secretes hCG. Doctors use hCG blood levels to help diagnose testicular cancer, monitor treatment response, and detect recurrence.
Testicular cancer isn’t the only malignancy that can produce hCG. Cancers of the liver, lung, pancreas, and stomach can also elevate levels. Because hCG is chemically similar to LH, men with naturally low testosterone (who produce high levels of LH as compensation) can sometimes show falsely elevated hCG readings. Marijuana use has also been associated with mildly elevated hCG, which can complicate interpretation. When hCG shows up unexpectedly in a blood test, doctors typically run additional tests to distinguish between these possibilities.