Why hCG Doubling Times Are Important in Early Pregnancy

When your prenatal health care provider talks about hCG, they're referring to human chorionic gonadotropin (aka "the pregnancy hormone"), which is produced by the placenta during pregnancy. The presence of hCG confirms a pregnancy, and measuring and monitoring hCG levels can help health care providers gather information about the fetus.

The levels of hCG in a pregnant person’s blood rise rapidly in early pregnancy, doubling every two to three days on average. This is known as hCG doubling time. When hCG levels don't rise as expected, it could be a cause for concern, but many pregnant people with lower-than-expected hCG levels or slower-than-average doubling times can go on to have healthy pregnancies and babies.

Here's what you need to know about testing for hCG, including what hCG doubling times can tell us and what they can't.

Testing hCG Levels

The two most common tests for hCG levels differ not only in how they are done but also what they can reveal.

• Qualitative test: This type of test only detects the presence of the hormone (around 12 to 14 days after conception). A urine test like the pee-on-a-stick pregnancy test available at drugstores is a qualitative test.
• Quantitative test: This determines the actual amount of the hormone in the body by testing a blood sample. A quantitative test (also known as a beta hCG test) can detect the hormone sooner, about 11 days after you conceive.

For a quantitative test, hCG is measured in milli-international units per milliliter (miU/ml). An hCG level above 5 mIU/ml is a positive indicator of pregnancy. Anything less than that is considered a negative pregnancy test.

While quantitative blood tests can be useful, not all health care providers routinely order them to confirm pregnancy. Many will use a transvaginal ultrasound to confirm the pregnancy instead.

In fact, a single quantitative hCG test value doesn't provide much information. These tests are typically repeated within the expected hCG doubling time window to see whether and how quickly hCG levels are increasing. This testing is usually done when there are concerns about the pregnancy, such as a history of miscarriage. Tests to monitor hCG levels are not typically needed for low-risk pregnancies.

Typical hCG Doubling Times

In a typical pregnancy, hCG levels double every 48 to 72 hours. This period increases to about every 96 hours as you get further along. HCG levels peak during the first eight to 11 weeks of pregnancy, then decline and plateau.

Healthy hCG levels can vary significantly from pregnancy to pregnancy, and there's a very wide range of what's considered normal. When health care providers monitor hCG levels, they're looking for the levels to fall within the expected range for gestational age and for the levels to double within the expected timeframe.

What hCG Doubling Times Can Show

Until about six or seven weeks after your last menstrual period, checking hCG doubling times is a good way to monitor whether a pregnancy is progressing normally. After that, ultrasounds become the best tool for getting information on how the pregnancy is developing, and they're more accurate than hCG numbers.

Causes of Slow-Rising hCG Levels

Slow-rising hCG doubling times can be a sign of miscarriage or a symptom of ectopic pregnancy, but this is not always the case. The two- to three-day doubling guideline holds true in 85% of normal pregnancies. That means that about 15% of viable pregnancies may have slower hCG doubling times.

Your hCG levels and doubling times alone aren't enough for your health care provider to diagnose miscarriage or ectopic pregnancy. They'll also consider any signs and symptoms you may be experiencing—such as vaginal bleeding, backache, or abdominal cramping—and run additional tests like getting an ultrasound image.

Causes of Higher-Than-Usual hCG levels

High hCG levels also have meaning. For example, they might indicate:

• Miscalculated conception date (you're farther along in your pregnancy than originally thought)
• Molar pregnancy
• Multiple pregnancy (being pregnant with two or more babies)

Finding out that your hCG levels are atypical can be very stressful and upsetting, so it's important to remember that slower (or faster) hCG doubling times don't always indicate an issue with your pregnancy.