How do hCG levels affect pregnancy?

Every healthy pregnancy requires hCG, the hormone that’s detected by a pregnancy test. Here’s what you need to know about hCG levels.

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If you’ve done a bit of reading—even just the back of the pregnancy test that you picked up at the drugstore—you have probably heard of hCG and might be wondering what it means for you. This primer has all the details, from what it is to how often it’s measured, along with everything you need to know about hCG levels that are too low, too high or just right.

What is hCG?

Short for human chorionic gonadotropin, hCG (also known as beta hCG) is a hormone produced by the outer layer of an early-pregnancy and pre-embryo structure called the blastocyst. This outer layer (named the trophoblast) provides the embryo with nutrients and later forms part of the placenta and fetal membranes, says Julia Kfouri, a maternal fetal medicine specialist at Mount Sinai Hospital and an assistant professor in the department of obstetrics and gynaecology at the University of Toronto. The hCG hormone is usually a sign of pregnancy, but it can also indicate an ectopic pregnancy, where a fertilized egg implants itself somewhere other than the uterus.

How is hCG measured?

Home pregnancy tests can detect hCG in urine, usually once it reaches 25 mIU/mL or higher, though “early detection” tests can detect the hormone in 10 mIU/mL. These tests don’t provide an exact reading of hCG levels; they simply confirm if your hCG levels are high enough to indicate pregnancy.

Blood tests are more sensitive, which means that they can detect pregnancy earlier than urine tests but by no more than a few days. You can only find out your exact hCG levels with a blood test, and the only reason you ever need to check your hCG levels is to confirm that you are actually pregnant. Unless you have pregnancy complications, you will never need to check your hCG levels again.

When will my hCG levels be measured?

A pregnant woman sees her doctor to ask about pregnancy hormones. How pregnancy hormones affect your body in each trimesterTypically, you will get a positive hCG result from a home pregnancy test or blood sample at your doctor’s office. This one-time measurement indicates that there is some trophoblastic tissue present, but it won’t confirm if your pregnancy is progressing normally, says Kfouri. You will then have a follow-up blood test around 48 to 72 hours later to check if your hCG levels are on the rise. If your hCG levels are in the normal range and the test confirms that they’re rising steadily, you won’t have your blood tested for hCG again unless you or your doctor suspects an ectopic pregnancy, a miscarriage or gestational trophoblastic disease (a severe and extremely rare condition involving tumours in the uterus that can occur during pregnancy or after a miscarriage, an abortion or a pregnancy).

What is considered to be healthy hCG levels?

Normal hCG levels vary widely among women, but healthcare practitioners still use the measurement as an indicator of approximate gestational age. In a healthy pregnancy, hCG levels will increase at least 50 percent every 48 hours, though it is more common for them to double every 48 hours. They typically peak at around 10 weeks. See below for the range of expected levels.

Estimated hCG levels during pregnancy (measured from the first day of the last menstrual period)

Less than 1 week 5 to 50 mIU/mL
1 to 2 weeks 50 to 500 mIU/mL
2 to 3 weeks 100 to 5,000 mIU/mL
3 to 4 weeks 500 to 10,000 mIU/mL
4 to 5 weeks 1,000 to 50,000 mIU/mL
5 to 6 weeks 10,000 to 100,000 mIU/mL
6 to 8 weeks 15,000 to 200,000 mIU/mL
8 to 12 weeks 10,000 to 100,000 mIU/mL

What does it mean if my hCG levels are too low?

Low hCG levels can simply be a sign of a very early pregnancy, but if they fail to increase a few days later, they could suggest an ectopic pregnancy. However, you would only know if your hCG levels fail to increase if you take a blood test and follow it up with a second blood test a few days later. They could also mean that a miscarriage has taken place. “If someone has a correct beta hCG rise early in the pregnancy and experiences vaginal bleeding at 10 or 11 weeks, the first thing we would do is request an ultrasound to characterize the pregnancy,” says Kfouri.

What if my hCG levels are too high?

High hCG levels could signal twins or triplets, but they can also be a symptom of gestational trophoblastic disease (GTD). If your early hCG reading is extremely high, you will need an immediate follow-up appointment to determine the cause. Your healthcare practitioner may also test your hCG levels later in the pregnancy if you experience hyperemesis gravidarum (severe morning sickness), a thyroid storm (a dangerous increase in heart rate, blood pressure and body temperature) and vaginal bleeding, all of which are possible signs of GTD.

When will my hCG levels go back to pre-pregnancy levels?

With a normal pregnancy, hCG will eventually become undetectable—typically by six weeks after delivery.

Read more:
When is it safe to announce your pregnancy?
88 things nobody tells you about being pregnant

 

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