hCG Levels Explained: Pregnancy, Testing, and What to Expect

HCG: What It Is and Why It Matters

The Role of hCG in Pregnancy

Human chorionic gonadotropin (hCG) is a crucial hormone during pregnancy. That holds especially true in its early stages. Its primary function is to stimulate the so-called corpus luteum, a temporary gland in the ovary, to produce a hormone known as progesterone.

Progesterone supports the growth of the lining of the uterus, reinforcing the endometrial walls and preventing menstrual bleeding, which is essential for maintaining a healthy pregnancy. This progesterone production is particularly critical during the first 3 to 4 weeks following implantation.

Throughout pregnancy, hCG also plays several other roles: 

• It promotes angiogenesis (the formation of new blood vessels) and ensures an adequate blood supply to the placenta. The placenta serves as the organ responsible for providing oxygen and nutrients to the developing fetus while removing waste products from the baby’s blood.
  
• Additionally, hCG helps regulate the immune response to prevent the body from rejecting the developing embryo.
  
• It has also been shown to aid in the development of fetal organs, such as the liver and kidneys, and even supports the growth of the umbilical cord.

How and When Your Body Produces hCG

Our bodies produce similar forms of hCG throughout life, even when not pregnant, although these levels are typically very low and not enough to be detected by pregnancy tests.

During pregnancy, hCG levels rise significantly, starting shortly after implantation.

• In the first trimester, hCG is primarily produced by the so-called villous syncytiotrophoblasts and trophoblastic cells, with the highest hCG levels by week 10.
  
• Throughout the second trimester and into the third, the placenta takes over hCG production, helping maintain optimal conditions for fetal development.

Why hCG Is Important for Early Pregnancy

As mentioned earlier, hCG is vital in early pregnancy because it stimulates progesterone production by the corpus luteum, which supports the uterine lining and prevents uterine contractions. It also aids in angiogenesis, ensures proper blood flow to the placenta, and helps regulate the immune response to protect the developing embryo.

Using hCG to Confirm Pregnancy

How to Test for hCG: Your Options

You can test for hCG in two ways: with a urine test at home (commonly called a pregnancy test) or with a blood test done at a doctor’s office.

• At-home urine hCG testing kits

These tests can confirm pregnancy by detecting elevated hCG levels, typically above 10-25 mIU/ml, depending on the brand. After the test, you’ll receive a positive (pregnant) or negative (not pregnant) result. It’s recommended to wait 12-14 days after conception before testing to avoid false negatives.

• Blood hCG tests
  
  The second way to test for hCG is through a blood test, often called a “beta hCG test,” done at your doctor’s office. This provides precise hCG levels in mIU/ml, unlike urine tests. Blood tests can detect hCG earlier—about a week after conception. They’re handy for couples with at-risk pregnancies, as regular monitoring can help ensure hCG levels are rising correctly, allowing for early intervention if needed.

When Does hCG Start to Show Up in Your Body?

hCG begins to appear around 6-8 days after conception. It can be detected in blood tests first, followed by urine tests a few days later.

HCG Levels Throughout Pregnancy

What hCG Levels Look Like Week by Week

hCG levels usually double every 48-72 hours, peaking during the first 8-11 weeks of pregnancy before gradually decreasing and stabilizing for the rest of the pregnancy. Here’s what hCG levels by weeks look like:

• hCG levels by day 21: 5-50 mIU/ml
• hCG levels at 4 weeks: 5-426 mIU/ml. 
• hCG levels at 5 weeks: 18-7,340 mIU/ml
• 6 weeks: 1,080-56,500 mIU/ml
• 7-8 weeks: 7,650-229,000 mIU/ml
• 9-12 weeks: 25,700-288,000 mIU/ml
• 13-16 weeks: 13,300-254,000 mIU/ml
• 17-24 weeks: 4,060-165,400 mIU/ml
• 25-40 weeks: 3,640-117,000 mIU/ml
  

It’s important to be aware that these numbers on this hCG levels chart serve only as guidelines; each woman’s hCG levels can vary. For instance, 4 weeks pregnant hCG levels can vary widely, as every pregnancy is unique. What truly matters is the change in those levels rather than the specific values themselves. Additionally, 2 weeks pregnant hCG levels may be undetectable by urine kits, as mentioned earlier.

For a more detailed breakdown, you can refer to an hCG levels chart by day to track the expected hormone progression throughout early pregnancy. There are also some online hCG levels calculators, which take into account factors like the date of your last menstrual period and your current hCG level.

How hCG Changes with Twins or More

If you are pregnant with twins or multiples, it’s common for your hCG levels to be higher than the typical range. Although there isn’t a specific chart indicating the maximum hCG levels for twin pregnancies, some doctors believe they can be 30-50% higher than those in a singleton pregnancy.

What Low hCG Levels Could Mean

Low hCG levels can indicate several potential issues:

• Miscalculation of Conception Date
  
  It’s possible you may have miscalculated when conception occurred. In this case, your hCG levels might seem low but are actually rising at the expected rate for your stage of pregnancy.

• Ectopic Pregnancy
  
  This occurs when a fertilized egg implants outside the uterus, often in a fallopian tube but sometimes in the ovaries or abdomen. Ectopic pregnancies can be life-threatening, especially if the fallopian tube ruptures. Seek immediate medical attention if you experience abnormal vaginal bleeding, lower back pain, or pelvic pain, as these are common early symptoms.

• Miscarriage
  
  Lower than normal hCG levels may signal a miscarriage, as the body halts hCG production during this event. Other symptoms include abdominal pain, back pain, unusual spotting or bleeding and/or passing fluid or tissue.

What to Know About High hCG Levels

If your hCG levels are higher than normal, it could mean several things:

Twins or multiples
As mentioned earlier, hCG levels for twins are usually more elevated. Some doctors estimate they can be 30-50% higher than in a single pregnancy, though there’s no exact number.

Miscalculated conception date
If your hCG levels seem high, you might be further along in your pregnancy than you thought. An ultrasound can help determine how far along you actually are.

Molar pregnancy
This happens when abnormal tissue grows in the uterus due to a genetic error. In a complete molar pregnancy, the placenta develops and produces hCG, but there’s no embryo. In a partial molar pregnancy, an embryo is present but has severe defects. Molar pregnancies need immediate medical attention and may also cause symptoms like vaginal bleeding, pelvic pain, and severe nausea.

Down syndrome
Higher hCG levels could suggest a risk of Down syndrome, but your doctor will need to do more tests, like bloodwork and ultrasounds, to assess the risk.

How Often Should You Check hCG Levels?

When to Test and Why Regular Monitoring Matters

HCG levels are usually only checked once or twice during pregnancy. Doctors typically measure them in the first trimester and don’t need to check again unless the initial levels are lower than expected. In that case, they will test again after a few days to compare the levels over time. Some genetic tests during pregnancy also use hCG levels to assess the risk of congenital disorders in the baby.

hCG and Fertility Treatments

How hCG Helps in Fertility Treatments

hCG is used in fertility treatments to trigger the release of eggs, similar to the hormone LH. It is easier to purify than LH and helps in ovulation induction, improving egg quality and supporting the luteal phase. It’s commonly used in treatments like IVF, IUI and egg freezing.

How hCG Levels Impact Fertility Treatment Success

hCG levels play a crucial role in fertility treatment success by indicating early pregnancy progress. 

After treatments like IVF, doctors monitor hCG levels to ensure they rise as expected, typically doubling every 48-72 hours. A steady increase signals healthy development, while slow or irregular rises may suggest complications like ectopic pregnancy or miscarriage. 

However, even low levels can lead to a successful pregnancy, with personalized monitoring and care crucial for guiding the outcome.

hCG After a Pregnancy Loss

What Happens to hCG Levels After a Miscarriage

After a miscarriage, hCG levels gradually decline as the body stops producing the hormone once the pregnancy ends. The rate at which hCG levels drop depends on how far along the pregnancy and the initial hCG levels at the time of miscarriage.

If the miscarriage occurs early and hCG levels are low, they can return to zero within a few days. For later miscarriages, when levels are higher, it may take several weeks for hCG to return to baseline. Once hCG levels reach zero (typically considered anything below five mIU/mL), menstruation and ovulation resume. 

Regarding ovulation, the Mira Hormone Monitor can be of great aid to let you know when your ovulation is back after a miscarriage.

What Can Affect Your hCG Levels?

External Factors That May Change Your hCG Readings

External factors that may change your hCG readings include:

Timing of the Test
Performing the test too early after conception can result in a false-negative due to low hCG levels.

Different hCG Isoforms
hCG exists in different isoforms, which are variants of the hormone with slightly different structures. Some pregnancy tests measure only specific isoforms. If the isoform present in the sample differs from what the test is designed to detect, it can lead to inaccurate results, particularly in urine tests.

High hCG Levels (Hook Effect)
The hook effect occurs when extremely high levels of hCG (usually above 500,000 mIU/mL) interfere with the assay’s ability to measure the hormone accurately. In such cases, the test may yield a false-negative result because the excess hCG saturates the binding sites of the antibodies used in the test, preventing proper detection.

Operator Error
This refers to mistakes made by the person conducting the test, such as not following instructions correctly or misreading the results. Home pregnancy tests are particularly susceptible to operator error. This can lead to false-positive or false-negative results.

Chemical Pregnancy
This term describes a very early miscarriage that occurs shortly after implantation. In this case, the body may still produce hCG, resulting in a positive pregnancy test. Unfortunately, though, the pregnancy is no longer viable in these cases.

Exogenous hCG
hCG used in fertility treatments or for athletic purposes may remain in the body for up to two weeks, affecting test results.

Tumors
Certain tumors can secrete hCG. This can lead to elevated levels that may mimic pregnancy.

Assay Interference
This refers to any external factor that affects the accuracy of hCG measurements. These factors may include the presence of specific antibodies or substances like biotin at high levels.

Familial hCG Syndrome
A rare genetic condition where hCG is continuously produced, leading to persistent positive results even in non-pregnant individuals.