hCG levels: Everything You Need to Know about the Pregnancy Hormone
hCG levels are the hormone of interest during pregnancy. After all, hCG levels are what pregnancy tests measure to tell you whether or not you’re pregnant. But, hCG levels can also be meaningful in understanding how your pregnancy is progressing. This post will cover:
- What is hCG?
- How do hCG levels rise normally during pregnancy?
- What does it mean if your hCG levels are too low or too high?
What is hCG?.
hCG, or human chorionic gonadotropin, is one of the major pregnancy hormones. Once implantation occurs, the placenta begins to form and secrete hCG. hCG levels rise and send a signal to the corpus luteum to keep producing progesterone, which in turn maintains the uterine lining (instead of shedding it and getting your period) and supports the developing embryo. For this reason, this hCG signal is sometimes called the “rescue of the corpus luteum.”
Do you have hCG levels when you are not pregnant?
Yes, but not in significant quantities. While hCG is typically considered the pregnancy hormone, every woman has very low levels of hCG (less than 5 IU/mL). However, hCG levels become meaningful once the placenta begins to secrete it in high amounts. So, unless you’re pregnant, you wouldn’t expect to see a positive pregnancy test because hCG levels would be too low for detection.
What level of hCG is considered pregnant?
When hCG levels rise to be greater than 25 IU/mL, then this is considered significantly higher than baseline, and a woman is considered pregnant.
What’s a normal hCG rising pattern?
After implantation occurs, hCG levels will double approximately every 48-72 hours. hCG levels will peak within the first 8-11 weeks of pregnancy, and then will begin dropping off from there and plateau for the remainder of pregnancy [1.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4584104/].
It’s important to know that the actual value of hCG levels isn’t as important as the pattern of hCG levels doubling every 48-72 hours. If you’ve experienced recurrent miscarriages or are a high-risk pregnancy, then your doctor may recommend a serial beta hCG test by testing your blood several times for hCG levels to see how quickly this hormone is being produced. However, unless there are signs of potential problems, hCG levels won’t be regularly checked after confirming you’re pregnant.
How do pregnancy tests detect hCG levels and determine if you’re pregnant?
Pregnancy tests are designed to detect changes in hCG levels using a scientific technique called sandwich enzyme immunoassay, and while this sounds complicated (and the biochemistry definitely is!), the principles are about as complicated as making a peanut butter and jelly sandwich.
hCG is a large molecule made of two separate components: the alpha part and the beta part. A pregnancy test comes with antibodies (aka “bread slices”) to detect the alpha part (“the peanut butter”) and the beta part (“the grape jelly”). So, if you take a pregnancy test and are pregnant, hCG in your urine will be sandwiched by the antibodies on the stick, and this sandwiching triggers the release of a dye, creating the dark line which indicates a positive pregnant test. The second line is a control test to make sure the antibodies are working.
Can you estimate hCG levels with a home pregnancy test?
While home pregnancy tests detect hCG in urine to determine if you’re pregnant, they cannot tell you the actual amount of hCG present. Because they are providing a qualitative result (aka yes or no), one thing to be mindful of is whether you are testing too often. So, if you test two days in a row, that may not be enough time for enough hCG to accumulate in your urine to generate a positive test, and the test results may look faint or negative.
Generally, based on the way home pregnancy tests work, the lines will start out faint and then get darker as pregnancy progresses and hCG levels rise until around week five of pregnancy, when the hook effect can happen. Check out the next section to learn about how false negative results can happen the further along you are in your pregnancy.
What do low hCG levels mean?
Low hCG levels can mean a few possible outcomes, and it’s important to consult with your doctor to know for sure:
- Miscalculation of pregnancy dating: How many weeks pregnant you are can be tricky to calculate because pregnancy begins at the time of implantation, but most doctors calculate pregnancy beginning from your last missed period (yes, they count it before you were even pregnant!) If you’re not sure when ovulation occurred, then pregnancy dating and the expected hCG levels may not be accurate. A more accurate way to date the pregnancy would be via ultrasound.
- Blighted ovum: This type of miscarriage happens when a fertilized egg does not develop into an embryo. So, while you might get a positive pregnancy test, hCG levels will not rise normally and stay low. Most of the time, causes of miscarriage are chromosomal abnormalities that happen due to random chance. So, getting pregnant after miscarriage, like after a blight ovum, is definitely possible.
- Ectopic pregnancy: If hCG levels are not rising normally or are rising erratically, then it’s possible that implantation has occurred outside of the uterus (aka ectopic pregnancy). Unfortunately, the embryo cannot be saved in this scenario and it’s important to seek medical consultation as soon as possible as rupturing of an ectopic pregnancy can result in serious health consequences for you.
What do high hCG levels mean?
High hCG levels can mean a few possible outcomes, and it’s important to consult with your doctor to know for sure:
- Miscalculation of pregnancy dating: As in the case of low hCG levels, miscalculating the pregnancy date can mean inaccurate expectations of hCG counts.
- Molar pregnancy: While not technically a form of miscarriage, a molar pregnancy is when defective placenta cells, which either grow too fast or around a non-viable embryo, continue secreting hCG. If you experience heavy bleeding in early pregnancy and have high hCG levels or experience high blood pressure in early pregnancy, then it’s possible that a molar pregnancy has occurred. It’s important to seek a medical professional right away in order to assess whether intervention to remove the abnormal cell growth is needed.
- Multiple pregnancy: If hCG levels are higher than expected, it’s possible that you could be pregnant with multiple embryos, meaning twins or more.
Can I use an LH test for also detecting hCG levels?
Potentially, yes. The molecular structure of LH is similar to the molecular structure of hCG, which means that LH tests cannot tell the difference between LH and hCG in your urine. So, if you’ve missed your period and have a positive LH test, then it’s possible that you’re pregnant, but it would be best to confirm with a pregnancy test specifically designed to measure hCG.