HCG, or human chorionic gonadotropin, is a hormone your body produces during pregnancy. It’s measured in milli-international units per milliliter (mIU/mL) through blood or urine tests, and the levels change dramatically week by week. In early pregnancy, hCG typically doubles every 1.4 to 3.5 days, rising from near zero to potentially over 200,000 mIU/mL by the end of the first trimester.
What hCG Does in Your Body
After a fertilized egg implants in the uterus, cells in the developing placenta begin releasing hCG into the bloodstream. The hormone’s primary job is to keep the corpus luteum, a temporary structure on the ovary, alive and producing progesterone. Progesterone reinforces the uterine lining and prevents menstrual bleeding, which is essential for the pregnancy to continue. Without hCG signaling, the corpus luteum would break down, progesterone would drop, and the uterine lining would shed.
By around weeks 8 to 12, the placenta itself takes over progesterone production and hCG levels begin to plateau or decline. This is why hCG is most clinically useful in the first trimester.
How hCG Is Measured
There are two main ways to check hCG. A qualitative urine test, the kind you buy at a pharmacy, simply tells you whether hCG is present above a threshold. Most home tests detect hCG at around 25 mIU/mL, which is why they work best after a missed period rather than immediately after conception. A quantitative blood test, sometimes called a beta hCG test, measures the exact concentration in your blood. This is the type doctors order when they need to track how levels are changing over time.
Blood tests are more sensitive and can detect pregnancy earlier. They’re also the only option when your care team needs a specific number to assess how a pregnancy is progressing.
Expected hCG Levels by Week
HCG levels vary enormously between individuals, so a single number on its own doesn’t tell the full story. The ranges below reflect typical blood levels during pregnancy, measured in mIU/mL:
- 4 weeks: 0 to 750
- 5 weeks: 200 to 7,000
- 6 weeks: 200 to 32,000
- 7 weeks: 3,000 to 160,000
- 8 to 12 weeks: 32,000 to 210,000
Notice how wide those ranges are. Two perfectly healthy pregnancies at six weeks could have hCG levels of 500 and 25,000. What matters more than any single reading is the trend: whether hCG is rising at the expected rate.
How Fast hCG Should Rise
In early pregnancy, hCG roughly doubles every two to three days, but the doubling time isn’t constant. Research published in the journal Fertility and Sterility found that doubling time actually slows as hCG concentrations increase and the pregnancy advances. At very early stages the doubling may happen in under two days; by seven or eight weeks, it takes longer.
Because of this natural slowdown, comparing two blood draws taken 48 hours apart is the standard approach. A rise of at least 35 to 50% over two days is generally considered reassuring in early pregnancy. After about eight weeks of gestation, the usual doubling rules become less reliable, and ultrasound becomes more informative.
When hCG Levels Are Lower Than Expected
A slow rise, a plateau, or a falling hCG level in the first eight to ten weeks can signal that something isn’t developing normally. Two common concerns are miscarriage and ectopic pregnancy, where the embryo implants outside the uterus.
However, hCG alone can’t distinguish between these possibilities. A study in Reproductive Sciences found that 90% of early ectopic pregnancies had hCG levels below 2,421 mIU/mL, which is the same range where many normal early pregnancies also fall. That’s why doctors combine serial hCG measurements with ultrasound. An ultrasound can typically visualize a gestational sac once hCG reaches around 2,400 to 3,000 mIU/mL. If hCG is above that level and nothing is visible in the uterus, ectopic pregnancy becomes a stronger concern.
Low or declining numbers are understandably alarming, but a single low reading doesn’t confirm a problem. The pattern over multiple tests, along with imaging, gives a much clearer picture.
When hCG Levels Are Higher Than Expected
Unusually high hCG can have several explanations. The most common is simply a twin or higher-order pregnancy, where more placental tissue produces more hormone. Another cause is a molar pregnancy, a rare condition where abnormal placental tissue grows rapidly. Extremely high hCG levels are a biological marker of molar pregnancy, sometimes exceeding 1,000,000 mIU/mL.
Very high hCG can also cause unexpected symptoms. The hCG molecule is structurally similar to thyroid-stimulating hormone, so at extreme concentrations it can stimulate the thyroid gland and temporarily increase thyroid hormone levels. This sometimes explains the exaggerated nausea or other hyperthyroid-like symptoms seen with molar pregnancies or twins.
hCG Outside of Pregnancy
HCG isn’t exclusively a pregnancy hormone. The pituitary gland produces small amounts, and levels below 5 mIU/mL are considered normal in non-pregnant individuals. Certain cancers can also produce hCG. Testicular germ cell tumors are the best-known example, where cancerous cells transform into placenta-like tissue and secrete the hormone. Elevated hCG also appears in some cancers of the liver, lung, pancreas, and stomach.
A few non-cancer factors can muddy the picture as well. In men, low testosterone can elevate luteinizing hormone, which cross-reacts with hCG on some lab tests and produces a falsely elevated reading. Marijuana use has also been associated with mildly elevated hCG levels.
Fertility Drugs and False Positives
If you’re undergoing fertility treatment, some medications contain hCG itself. These “trigger shots” are used to induce ovulation, and they introduce hCG directly into your system. After receiving one, hCG can remain detectable for 10 to 14 days, meaning a pregnancy test taken too soon may reflect the medication rather than an actual pregnancy. Your fertility clinic will typically tell you exactly when to test to avoid this confusion.
How Long hCG Takes to Clear After a Loss
After a miscarriage, ectopic pregnancy, or delivery, hCG doesn’t disappear overnight. Research from the University of Pennsylvania found that hCG levels typically drop 35 to 50% within two days and 66 to 87% within seven days when a pregnancy is resolving on its own. The starting level matters: a pregnancy that reached high hCG concentrations will take longer to return to undetectable levels (below 5 mIU/mL) than one that ended very early.
For most early pregnancy losses, hCG clears within a few weeks. After a molar pregnancy or later-term loss, the timeline can stretch longer. Persistent or rising hCG after a known loss requires further evaluation, because it can indicate retained tissue or, rarely, a condition called gestational trophoblastic neoplasia.