An hCG blood test measures the level of human chorionic gonadotropin in your blood, a hormone produced almost exclusively during pregnancy. It’s more sensitive than a home urine test and can detect pregnancy earlier, but it’s also used to monitor pregnancy health, screen for certain complications, and occasionally help diagnose conditions unrelated to pregnancy. A result below 5 mIU/mL is considered negative for pregnancy, while anything above that range warrants follow-up.
What hCG Does in the Body
hCG is produced by the tissue that eventually becomes the placenta, starting shortly after a fertilized egg implants in the uterus. Its main job is to keep the corpus luteum alive during early pregnancy. The corpus luteum is a temporary structure in the ovary that produces progesterone, the hormone responsible for maintaining the uterine lining so the embryo can develop. Without hCG, progesterone levels would drop and the pregnancy couldn’t continue.
The pituitary gland, liver, and colon also produce tiny amounts of hCG outside of pregnancy, which is why healthy men and non-pregnant women can have very low, detectable levels. In men, a normal level is below 2 mIU/mL. In non-pregnant women, it’s below 5 mIU/mL.
Two Types of hCG Blood Tests
There are two versions of this test, and they answer different questions.
A qualitative hCG blood test gives a simple yes or no: is hCG present above the threshold that indicates pregnancy? This is essentially a more sensitive version of a home pregnancy test.
A quantitative hCG blood test (sometimes called a beta hCG test) measures the exact amount of hCG in your blood. This is the version doctors order when they need to track how a pregnancy is progressing, because the specific number and how it changes over time can reveal problems that a simple positive or negative result would miss.
When the Test Can Detect Pregnancy
hCG levels start building once the fertilized egg implants in the uterus, roughly 6 to 10 days after conception. A blood test can often pick up hCG as early as 10 days after conception, several days before a missed period. Home urine tests typically need higher hCG concentrations to register a positive, which is why blood tests can confirm pregnancy sooner.
At 3 weeks after the last menstrual period (about one week after conception), hCG levels range from just 5 to 72 mIU/mL. That’s a very small amount, and it’s the reason timing matters. Testing too early, even with a blood draw, can produce a false negative simply because the embryo hasn’t had enough time to produce detectable levels.
How hCG Levels Change Week by Week
In a healthy pregnancy, hCG rises steeply through the first trimester, peaks around weeks 8 to 12, and then gradually declines for the rest of the pregnancy. The ranges at each stage are wide, so a single number doesn’t tell you much on its own. What matters more is the trend over multiple tests.
Here’s a general guide to expected levels based on weeks since the last menstrual period:
- 4 weeks: 5 to 426 mIU/mL
- 5 weeks: 18 to 7,340 mIU/mL
- 6 weeks: 1,080 to 56,500 mIU/mL
- 7 to 8 weeks: 7,650 to 229,000 mIU/mL
- 9 to 12 weeks: 25,700 to 288,000 mIU/mL
- 13 to 16 weeks: 13,300 to 254,000 mIU/mL
- 17 to 24 weeks: 4,060 to 165,400 mIU/mL
- 25 to 40 weeks: 3,640 to 117,000 mIU/mL
These ranges vary significantly from person to person. A level of 30,000 mIU/mL at 8 weeks is normal, and so is 200,000 mIU/mL at 8 weeks. The absolute number is less important than whether it’s following the expected upward or downward pattern for your stage of pregnancy.
What Doctors Look for in Serial Tests
In early pregnancy, doctors often order two hCG blood draws 48 hours apart to see whether levels are rising appropriately. In a viable pregnancy, hCG typically increases by at least 66% over that 48-hour window, with a median increase of about 124% (roughly doubling). The doubling time isn’t constant, though. It’s fastest in very early pregnancy and gradually slows as hCG concentrations climb and gestational age increases. Doubling times in the literature range from about 1.4 to 3.5 days.
A rise of less than 66% over 48 hours raises concern for a possible ectopic pregnancy, where the embryo implants outside the uterus. A drop in hCG of more than 50% over 48 hours is strongly suggestive of a miscarriage. These patterns aren’t absolute, as roughly 15% of normal pregnancies can show an hCG pattern that initially looks abnormal, but they give doctors critical information for deciding what to investigate next, usually with ultrasound.
Reasons for the Test Beyond Pregnancy
While pregnancy is the most common reason for an hCG blood test, it’s not the only one. Elevated hCG in men or non-pregnant women can be a marker for certain cancers, particularly germ cell tumors of the ovaries or testes. These include conditions like choriocarcinoma, dysgerminoma, and embryonal carcinoma. In these cases, hCG functions as a tumor marker, and serial measurements help track whether treatment is working.
Many other cancers can also produce hCG or its subunits in smaller quantities, including cancers of the lung, bladder, kidney, stomach, pancreas, and breast. When hCG shows up in these contexts, it’s often considered an unfavorable sign for prognosis. Postmenopausal women can also have mildly elevated hCG from pituitary production, which is normal and shouldn’t be confused with disease.
Gestational trophoblastic disease is another important reason for hCG monitoring. This group of conditions involves abnormal growth of the tissue that normally forms the placenta. Levels can be mildly elevated or extremely high depending on the specific type, and tracking hCG after treatment is essential because a rising level indicates the disease hasn’t been fully cleared.
What Can Affect Your Results
A few situations can produce misleading hCG levels. The most straightforward is fertility treatment. hCG injections are commonly used to trigger ovulation, and these injections will cause elevated hCG on a blood test for days afterward. If you’re testing for pregnancy during a fertility treatment cycle, your doctor will time the blood draw to avoid picking up residual medication.
hCG has also been marketed (without medical evidence) as a weight-loss supplement. Anyone using these products could test positive for pregnancy or show elevated levels on a blood test. Athletes sometimes use hCG to stimulate testosterone production, which would similarly affect results.
Timing is the other major factor. Testing too early after conception can give a false negative, and a single low-positive result in the 5 to 25 mIU/mL range is often considered indeterminate. In that gray zone, a repeat test 48 to 72 hours later clarifies whether levels are trending up (likely early pregnancy) or down (likely not viable or not pregnant).