HCG, or human chorionic gonadotropin, is a hormone your body produces during pregnancy. Its levels in your blood or urine tell you whether you’re pregnant, roughly how far along you are, and whether the pregnancy is progressing normally. A single number on its own means less than the pattern of how that number changes over time, which is why doctors often order repeat tests 48 hours apart rather than drawing conclusions from one result.
What HCG Does in Early Pregnancy
After a fertilized egg implants in the uterine wall, the developing placenta starts releasing hCG into your bloodstream. This hormone’s primary job is to keep the corpus luteum, a temporary structure in the ovary, alive and producing progesterone. Progesterone thickens the uterine lining and prevents your body from shedding it, which is what would otherwise trigger a period. The corpus luteum handles progesterone production for roughly the first 12 weeks of pregnancy, at which point the placenta takes over.
Normal HCG Levels by Week
HCG levels vary enormously from person to person, even in perfectly healthy pregnancies. What matters more than hitting a specific number is falling somewhere within the expected range for your gestational age. These ranges are measured in mIU/mL (milli-international units per milliliter) and are counted from the first day of your last menstrual period:
- Week 3: 5 to 50
- Week 4: 5 to 426
- Week 5: 18 to 7,340
- Week 6: 1,080 to 56,500
- Weeks 7 to 8: 7,650 to 229,000
- Weeks 9 to 12: 25,700 to 288,000
Notice how wide those ranges are. At week 5, one healthy pregnancy might show an hCG of 200 while another shows 5,000. That’s why comparing your numbers to someone else’s is not useful.
How Fast HCG Should Rise
In early pregnancy, hCG levels roughly double every 48 to 72 hours. As levels climb higher, the doubling slows to about every 96 hours. Doctors don’t expect an exact doubling. The minimum expected rise over 48 hours depends on where you’re starting: about 49% when hCG is below 1,500, about 40% when it’s between 1,500 and 3,000, and about 33% when it’s above 3,000. Research suggests that a rise of at least 35% over two days is the lower threshold for a viable pregnancy.
This is why serial blood draws matter. A single hCG number is a snapshot. Two or three numbers taken 48 hours apart reveal a trend, and the trend is what tells you whether the pregnancy is developing normally.
When HCG Peaks and Drops
HCG levels typically peak somewhere between weeks 9 and 12, often reaching into the hundreds of thousands. After that peak, levels gradually decline through the second and third trimesters. This drop is completely normal. By that point, the placenta has taken over hormone production and hCG has done its job. If you’ve ever heard of morning sickness improving around the end of the first trimester, the declining hCG is part of the reason.
What Lower-Than-Expected Levels Mean
Low hCG doesn’t automatically mean something is wrong, but it does prompt further investigation. The most common and least concerning explanation is simply wrong dates. If you have irregular cycles or aren’t sure when your last period started, you might be a few days earlier than you think, and a few days makes a huge difference in early pregnancy hCG ranges.
When low levels are accompanied by slow or stalling rises, the possible causes include:
- Miscarriage or threatened miscarriage: Because the placenta produces hCG, a pregnancy that stops developing will show declining or plateauing levels. Most miscarriages occur before the 20th week.
- Blighted ovum: The fertilized egg implants and a gestational sac forms, but the embryo never develops. HCG may rise initially but won’t keep climbing normally.
- Ectopic pregnancy: When the embryo implants outside the uterus, typically in a fallopian tube, hCG levels are usually lower than expected and rise more slowly. This is a medical emergency that needs prompt treatment.
A single low reading is never enough to diagnose any of these. Doctors typically order repeat hCG tests every two to three days and combine the results with an ultrasound to get the full picture.
What Higher-Than-Expected Levels Mean
Unusually high hCG can also have benign or serious explanations. Carrying twins or multiples naturally produces more hCG because there’s more placental tissue making the hormone. If your levels are running well above the expected range and an ultrasound shows two gestational sacs, that’s the likely answer.
A more concerning cause is a molar pregnancy (hydatidiform mole), where abnormal placental tissue grows instead of a normal embryo. About 50% of complete molar pregnancies produce hCG levels above 100,000 mIU/mL before treatment, which is markedly higher than most normal pregnancies at the same stage. Partial molar pregnancies tend to produce lower levels; fewer than 10% reach that 100,000 threshold. Molar pregnancies require medical treatment and monitoring afterward to ensure hCG returns to zero.
Blood Tests vs. Home Pregnancy Tests
Home pregnancy tests detect hCG in urine and turn positive once levels reach about 20 to 25 mIU/mL. That’s sensitive enough to catch most pregnancies around the time of a missed period, but early testing before your period is due can easily produce a false negative simply because levels haven’t climbed high enough yet. Different brands also vary in sensitivity, which is why one test might show a faint line while another shows nothing on the same day.
A quantitative blood test (sometimes called a “beta hCG”) can detect levels below 10 mIU/mL, picking up pregnancy two to four days earlier than a urine test. More importantly, blood tests give you an exact number, which is what allows doctors to track the doubling pattern and spot problems early. Urine tests only tell you yes or no.
How Long HCG Stays After a Loss
After a miscarriage, hCG doesn’t disappear overnight. A 2013 study of 443 women found that levels dropped 35 to 50 percent within two days after the pregnancy ended and 66 to 87 percent within seven days. That’s faster than previously thought, but it still means a home pregnancy test can show positive for one to several weeks after a loss. This doesn’t mean you’re still pregnant. It means the hormone is clearing from your system at its own pace.
HCG Outside of Pregnancy
A positive hCG result when you’re not pregnant (or in men) is uncommon but has specific medical causes. Certain cancers, including ovarian, testicular, breast, lung, and gastrointestinal tumors, can produce hCG as a byproduct. The pituitary gland can also release small amounts in rare cases. Additionally, a phenomenon called “phantom hCG” occurs when antibodies in the blood interfere with the test itself, producing a false positive. This happens in an estimated 1 in 1,000 to 1 in 10,000 blood tests.
Fertility medications that contain hCG can also cause positive results. These are injectable drugs used to trigger ovulation during fertility treatment. If you’ve recently had an hCG injection as part of a treatment cycle, your doctor will typically advise you to wait a specific number of days before testing so the injected hormone has time to clear and any positive result reflects an actual pregnancy.
HCG has also been marketed for weight loss and used by some athletes to boost testosterone production, both of which would cause detectable levels on a pregnancy test. The weight loss use has no scientific backing and is not approved for that purpose.