Question: 

I’m newly pregnant and my doctor wants to test my hCG levels. What is hCG, and why does it need to be checked?

Answered by Karen Carlson, MD, OB-GYN:

Human chorionic gonadotropin, or hCG, is often called the “pregnancy hormone.” If you’ve ever taken a home pregnancy test, you’ve tested for hCG. Let me explain what this hormone does and why it’s so important in early pregnancy.

What is hCG?

HCG is a hormone made during pregnancy by cells that eventually form the placenta. Your body starts making hCG shortly after a fertilized egg implants in the uterus. This happens about six to 12 days after conception. Because hCG shows up so early, it’s one of the first signals that your body is pregnant.

The hormone can be detected in both your blood and urine, which is how pregnancy tests work. When you see a positive result on a home pregnancy test, it’s because the test has detected hCG in your urine.

Why hCG is important in early pregnancy

Early in pregnancy, hCG has a crucial job. It supports the corpus luteum in your ovary, which allows your body to keep producing progesterone. Progesterone is essential because it maintains the uterine lining and supports early pregnancy and placental development. Without enough progesterone, the pregnancy cannot continue.

How hCG levels change

HCG levels typically rise very quickly in the first trimester. In a healthy early pregnancy, hCG often doubles every 48 to 72 hours. This rapid rise is normal and expected.

Health care providers often look at the trending levels of hCG rather than a single value. By seeing how your hCG levels change over time, they can help assess whether your pregnancy is progressing normally. For example, if hCG levels don’t rise as expected, it might signal a problem that needs attention.

Later in pregnancy, hCG levels naturally plateau and then decline. This is completely normal and doesn’t mean anything is wrong.

HCG and morning sickness

Rising hCG levels are thought to play a key role in pregnancy-related nausea and vomiting, commonly known as “morning sickness.” You might notice that symptoms often peak when hCG levels are at their highest, usually in the first trimester. For most women, nausea improves as hCG levels level off in the second trimester.

Other uses for hCG

Outside of pregnancy, hCG is sometimes used as an injection in fertility treatments to trigger ovulation. This can help women who are trying to conceive.

While hCG is normally associated with pregnancy, it’s worth knowing that certain rare tumors, such as some testicular or ovarian cancers, can also produce this hormone. If someone has unusually high levels of hCG outside of pregnancy, it can provide an important clue for doctors to investigate further.