Why Are My hCG Levels Low or Dropping?

Human chorionic gonadotropin (hCG) is a hormone produced by the placenta during pregnancy. If hCG levels fall or plateau early in the first trimester, doctors may suspect a potential pregnancy loss. That's because miscarriage, ectopic pregnancy, and blighted ovum are associated with low or slow-rising hCG levels.

It's important to note, however, that there's a wide range of normal when it comes to hCG levels in early pregnancy, and sometimes unusual numbers aren't a cause for concern. You can experience dropped hCG levels and not miscarry, and a healthy baby might still result from a pregnancy with lower-than-expected hCG levels.

Here's everything you need to know about tracking hCG levels during pregnancy, including the link between dropping or low hCG levels and miscarriage.

How hCG Is Measured

Home pregnancy tests work by detecting hCG, a hormone that's only produced during pregnancy, in your urine. But while these pregnancy tests can evaluate the presence of hCG, they can't give an exact level. For that, you'll need a quantitative hCG blood test, usually given in a doctor's office.

Your provider might request serial hCG measurements, taken between two and three days apart in the early first trimester, to see how quickly hCG is doubling. This is done to rule out miscarriage, ectopic pregnancy, and/or chemical pregnancy.

Serial testing provides more useful information than a single hCG level, as it shows trends in your hCG measurements.

Normal hCG Levels in Pregnancy

During the first few weeks of pregnancy, hCG levels rise dramatically, usually doubling every two to three days.

Your hCG levels peak about 8 to 10 weeks into the pregnancy, and then they slow down and level off, according to Brennan Lang, MD, FACOG, an OB-GYN at the Texas Children's Pavilion for Women.

The below ranges give an idea of what's considered normal.

What Do Low hCG Levels Mean?

There's a wide range of normal when it comes to hCG levels, so high or low numbers aren't always cause for concern. That said, too-low numbers—or numbers that start dwindling or plateauing before they should—may raise red flags.

It's possible that your pregnancy isn't as far along as previously thought. But you could also be experiencing a miscarriage, a blighted ovum (empty gestational sac), or an ectopic pregnancy (when a fertilized egg implants somewhere outside the uterus, usually in the fallopian tube).

What If hCG Levels Are Increasing But Not Doubling?

Everyone is different, and hCG levels can fluctuate without indicating a larger issue. For instance, one study that monitored hCG patterns in healthy pregnancies found that the lowest documented two-day hCG increase was just 53%.

This means an hCG level increase of about 75% (rather than by 100%, which is doubling) after three days could still be normal. If your hCG levels aren't exactly doubling but are still increasing, that might still be a good sign.

Because of these natural variations, hCG patterns alone can't determine whether or not your pregnancy is viable. Hormone testing should always be followed up by an ultrasound before a diagnosis is made.

Do Lowering hCG Levels Indicate a Miscarriage?

If hCG levels aren't rising as expected—or if you're experiencing symptoms of miscarriage—a health care provider may call for two hCG blood tests about 48 hours apart. These are called serial hCG measurements. Comparing the results will let them see trends in your hCG levels.

HCG levels during miscarriage "usually fall, plateau, or rise abnormally slow," says Dr. Lang. He clarifies that a "slow" rise is considered less than 35% over 48 hours in early pregnancy.

But while these trends can signal miscarriage, most of the time, "you have to wait until a pregnancy can be seen on ultrasound around six weeks to confirm things are going normally," says Maureen Baldwin, MD, MPH, an assistant professor of Obstetrics and Gynecology at Oregon Health & Science University.

Due to low or falling hCG levels, you might need some additional tests, such as progesterone blood tests. A transvaginal ultrasound might also be recommended to look for a gestational sac and monitor fetal development.

Aside from miscarriage, abnormally low hCG levels could also indicate an ectopic pregnancy or a blighted ovum.

How Long Until hCG Falls to Zero After Miscarriage?

After experiencing a miscarriage, your hCG levels will continue to decrease. They should return to baseline levels anywhere from 7 to 60 days after the miscarriage, depending on how far along the pregnancy was. Those who miscarry earlier in pregnancy will generally see a quicker return to pre-pregnancy hCG levels.

"After a miscarriage has been completed, there is not typically any need to monitor hCG levels," says Dr. Baldwin. "If a home urine pregnancy test is still positive after a month, or if you still feel pregnant after a week, you should speak with your provider."

Trying to Conceive After Miscarriage

If you want to try to conceive again after a miscarriage, it's ideal to wait until your hCG level has dropped to either zero or an undetectable level—but there's no need to wait any longer unless you choose to do so. This hormone readjustment signals that the uterine lining is back to normal and can receive a newly fertilized egg. 

Also, elevated hCG levels after miscarriage could return a false positive pregnancy test, which is something to keep in mind when trying to conceive again.

Ask your doctor how long you should wait before trying for another child, as recommendations vary depending on multiple factors, including the specifics of your miscarriage and your medical history.

In the past, it was routine for medical professionals to recommend waiting at least three to six months after pregnancy loss before trying again. However, studies now show that the chance of conception might be higher for those who begin trying sooner than three months after pregnancy loss.

Additional reporting by Krissi Danielsson.