HCG, or human chorionic gonadotropin, is a hormone your body produces during pregnancy. It’s the hormone that pregnancy tests detect, and its levels rise rapidly in early pregnancy, typically doubling every 48 hours before peaking between weeks 8 and 12. Tracking hCG levels helps confirm a pregnancy is progressing normally and can flag potential complications early.
What hCG Does in Early Pregnancy
As soon as a fertilized egg implants in the uterine wall, the developing placenta begins releasing hCG into your bloodstream. This hormone has one critical early job: keeping the corpus luteum alive. The corpus luteum is a temporary structure in the ovary that produces progesterone, the hormone responsible for maintaining the uterine lining so the pregnancy can continue.
Without hCG, the corpus luteum would break down, progesterone would drop, and the uterine lining would shed. HCG keeps that from happening until about six weeks of gestation, when the placenta itself takes over progesterone production. After that handoff, hCG is no longer needed for progesterone support, which is part of why levels eventually decline.
Normal hCG Levels by Week
HCG levels vary enormously from one person to another, even in perfectly healthy pregnancies. What matters more than any single number is how quickly your levels are rising. That said, here are the typical ranges based on weeks since your last menstrual period (LMP):
- Week 3: 5 to 50 mIU/mL
- Week 4: 5 to 426 mIU/mL
- Week 5: 18 to 7,340 mIU/mL
- Week 6: 1,080 to 56,500 mIU/mL
- Weeks 7 to 8: 7,650 to 229,000 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 wide those ranges are. At week 5, one healthy pregnancy might measure 18 mIU/mL while another measures over 7,000. Both can be completely normal. The pattern of change over time is far more meaningful than any single reading.
How Fast hCG Should Rise
In a healthy early pregnancy, hCG levels roughly double every 48 hours. But the actual expected rate of increase depends on where your levels currently sit. When hCG is below 1,500 mIU/mL, it should rise by at least 49% over 48 hours. Between 1,500 and 3,000 mIU/mL, a minimum 40% increase is expected. Above 3,000 mIU/mL, the minimum drops to about 33% over 48 hours.
This slowing is normal. As levels climb higher, the doubling time naturally stretches out. By the time hCG reaches its peak between weeks 8 and 12 (often in the range of 32,000 to 210,000 mIU/mL), the rapid doubling phase is long over. After the first trimester, levels gradually decline and stay lower for the remainder of the pregnancy.
This is why your provider may order two blood draws spaced 48 hours apart rather than relying on a single number. One reading tells you very little on its own. Two readings reveal whether the trajectory looks right.
How hCG Is Measured
There are three ways to check hCG, and they differ significantly in what they can tell you.
Home urine tests are qualitative: they give you a yes or no answer. But not all tests are equally sensitive. The most sensitive home test (First Response Early Result) can detect hCG at concentrations as low as 6.3 mIU/mL, catching over 95% of pregnancies on the day of a missed period. Other popular brands require 25 mIU/mL or more, detecting about 80% of pregnancies at that point. Several brands on the market don’t reliably detect hCG until it reaches 100 mIU/mL, which means they miss the majority of pregnancies on the day of a missed period. If you test early and get a negative result, the test’s sensitivity may be the reason.
A qualitative blood test works similarly to a home test, flagging hCG at a threshold of roughly 10 to 25 mIU/mL. A quantitative blood test is the most precise option, measuring the exact concentration of hCG down to about 1 mIU/mL. This is the type your provider uses when tracking how levels change over time.
What Low or Slow-Rising Levels Can Mean
HCG that fails to double within 48 hours can point to a few different situations. The most common are miscarriage and ectopic pregnancy (where the embryo implants outside the uterus, usually in a fallopian tube). It can also simply mean you’re earlier in pregnancy than you thought, which shifts the expected range downward.
An ectopic pregnancy is particularly important to identify quickly because it can become a medical emergency. One key indicator is hCG that rises too slowly to fit a normal pattern. Levels that plateau or rise sluggishly rather than doubling prompt your provider to investigate further, typically with ultrasound.
A single low reading on its own is not a diagnosis. Plenty of healthy pregnancies start with hCG in the low end of the normal range. The concern arises when repeat testing shows the expected rise isn’t happening.
What Unusually High Levels Can Mean
HCG levels higher than expected for your gestational age can also carry meaning. The most straightforward explanation is a multiple pregnancy: twins or triplets produce more hCG because there’s more placental tissue. You may also be further along than estimated.
In rarer cases, extremely high hCG can indicate a molar pregnancy, a condition where abnormal placental tissue grows instead of (or alongside) a normal embryo. Complete molar pregnancies commonly produce hCG concentrations above 100,000 mIU/mL. High hCG alone doesn’t confirm a molar pregnancy, but it’s one of the findings that triggers closer evaluation.
How Long hCG Stays in Your System
After a pregnancy ends, whether through delivery, miscarriage, or other loss, hCG doesn’t disappear immediately. Your body needs time to clear it. After an early miscarriage, hCG can drop to undetectable levels within days. After a later loss or a full-term delivery, it can take up to six weeks for levels to return to their pre-pregnancy baseline (below 5 mIU/mL).
This is why a home pregnancy test can still show positive for weeks after a pregnancy loss. It doesn’t mean you’re still pregnant. It means hCG hasn’t fully cleared yet. If your provider is monitoring you after a loss, they’ll track quantitative hCG levels to confirm a steady decline toward zero. HCG that plateaus or rises again after a loss warrants further investigation.