HCG, or human chorionic gonadotropin, is a hormone produced during pregnancy that can be measured through blood or urine tests. In early pregnancy, hCG levels start as low as 5 mIU/mL around week 3, rise rapidly to a peak of roughly 50,000 to 100,000 mIU/mL by weeks 8 to 10, then gradually decline for the rest of the pregnancy. These levels are what pregnancy tests detect, and they’re also what doctors track to confirm a pregnancy is progressing normally.
What hCG Does in Early Pregnancy
HCG is produced by the outer layer of cells that eventually forms the placenta. Its main job in the first several weeks is to keep the corpus luteum, a temporary structure on the ovary, alive and functioning. The corpus luteum produces progesterone, estrogen, and other hormones that sustain the pregnancy until the placenta is developed enough to take over hormone production on its own, usually around weeks 8 to 10.
HCG works by mimicking another hormone called LH (luteinizing hormone), which your body normally uses during the menstrual cycle. Because the two hormones are structurally similar, hCG can bind to the same receptors and keep progesterone flowing when it matters most. Without adequate hCG in those early weeks, progesterone drops and the uterine lining can’t support the embryo.
Normal hCG Levels by Week
HCG ranges are wide at every stage of pregnancy, which is one of the most important things to understand about them. Two healthy pregnancies at the same gestational age can have dramatically different numbers. What matters more than any single reading is the trend over time. Here are typical ranges based on weeks since the last menstrual period:
- Week 3: 5 to 72 mIU/mL
- Week 4: 10 to 708 mIU/mL
- Week 5: 217 to 8,245 mIU/mL
- Week 6: 152 to 32,177 mIU/mL
- Weeks 7 to 8: 4,059 to 153,767 mIU/mL
- Weeks 9 to 12: 25,700 to 288,000 mIU/mL
- Weeks 13 to 16: 13,300 to 254,000 mIU/mL
- Weeks 17 to 24: 4,060 to 165,400 mIU/mL
- Weeks 25 to 40: 3,640 to 117,000 mIU/mL
Notice how the ranges overlap heavily between weeks. A reading of 30,000 mIU/mL could be normal at week 6, week 10, or week 14. That’s why a single hCG number without context, including accurate dating, tells you very little.
How Fast hCG Should Rise
In a healthy early pregnancy, hCG levels roughly double every 1.4 to 2.1 days. But the doubling rate slows as levels climb higher. When hCG is below 1,500 mIU/mL, the minimum expected increase over two days is about 49%. At levels between 1,500 and 3,000, the minimum two-day rise drops to 40%. Above 3,000, it slows further to around 33%.
This matters because doctors often order two blood draws 48 hours apart to see whether hCG is rising at the expected rate. A single number in the “normal” range doesn’t confirm a viable pregnancy on its own. The rate of change is the more telling piece of the puzzle. Once hCG passes roughly 50,000 to 100,000 mIU/mL (typically around weeks 8 to 10), levels plateau and then start declining. This is completely normal and doesn’t signal a problem.
Blood Tests vs. Home Pregnancy Tests
Home urine pregnancy tests typically detect hCG at a threshold of about 25 mIU/mL, which means they can pick up a pregnancy around the time of a missed period (roughly week 4). Testing earlier than that often produces a negative result simply because hCG hasn’t accumulated enough in urine yet.
A quantitative blood test (sometimes called a beta hCG test) measures the exact concentration of hCG in your bloodstream. Blood tests are more sensitive, can detect pregnancy slightly earlier, and provide a specific number rather than a yes/no answer. This is why doctors use serial blood draws to monitor early pregnancies, especially after fertility treatments or when there’s a concern about viability.
One unusual quirk worth knowing: at extremely high hCG concentrations (above 500,000 mIU/mL), a phenomenon called the “hook effect” can overwhelm the test and produce a false negative. This is rare and mainly occurs in molar pregnancies, where hCG levels climb far beyond the normal range.
What Low hCG Levels Can Mean
A slow rise in hCG, or levels that start to fall during the first 8 to 10 weeks, suggests that the pregnancy tissue is no longer growing normally. This pattern can indicate a miscarriage in progress or an ectopic pregnancy (where the embryo implants outside the uterus, most often in a fallopian tube).
However, a single “low” reading doesn’t automatically mean something is wrong. If your dates are off by even a few days, your expected range shifts significantly. A level that looks low for six weeks might be perfectly appropriate for five weeks and four days. This is why follow-up testing matters more than a snapshot. Doctors look at the trajectory: is hCG rising appropriately, plateauing too early, or falling?
What High hCG Levels Can Mean
Higher-than-expected hCG has a few possible explanations. The most common is simply inaccurate dating. If you’re further along than you think, your numbers will look elevated for the week you believe you’re in.
Twin or other multiple pregnancies also produce higher hCG because there’s more pregnancy tissue generating the hormone. In rarer cases, very high hCG points to a molar pregnancy, a condition where abnormal placental tissue grows rapidly instead of a normal embryo. Molar pregnancies produce distinctly elevated numbers. Research comparing molar and non-molar failed pregnancies found that hCG above 16,435 mIU/mL at 6 to 7 weeks, above 64,911 at 8 to 9 weeks, or above 126,278 at 10 to 11 weeks was most commonly associated with a complete molar pregnancy.
hCG Outside of Pregnancy
In men and non-pregnant women, hCG levels are normally very low or undetectable. When hCG shows up outside of pregnancy, it can be a tumor marker. Certain cancers, particularly germ cell tumors of the ovaries or testes, produce hCG. This is why an hCG blood test is sometimes ordered as part of cancer screening or monitoring, not just for pregnancy-related reasons.
HCG can also be mildly elevated in perimenopausal and postmenopausal women due to small amounts produced by the pituitary gland. These levels are typically very low (under 10 mIU/mL) and not a cause for concern on their own.