Human chorionic gonadotrophin (hCG for short) is the unique pregnancy hormone that is produced by the cells of the placenta. hCG is needed to maintain the pregnancy and it also aids with fetal development. Experts theorize that this special hormone also plays a role in suppressing a pregnant woman’s immune system (so that her body doesn’t reject the developing baby as an “intruder.”)
Over-the-counter home pregnancy tests work by checking for the presence of hCG in a woman’s urine. If there’s any hCG in a woman’s body, she is indeed pregnant. Although hCG has been building up since conception, a urine pregnancy test won’t be able to pick up any hCG levels until 12 to 14 days after conception – around the time of a woman’s missed period.
Blood tests can also check for hCG to confirm pregnancy. In 5 percent of all pregnant women, levels of hCG can be detected in the blood at 8 days after conception – before the woman misses her period. For the other 95 percent of expectant mothers, a blood test can detect hCG levels by 11 days after she’s conceived.
Why is hCG Detected in the Blood First?
To answer this question, you have to understand some basics of conception.
During conception, your egg is fertilized by your partner’s sperm in the fallopian tube. Afterwards, your future baby (which is just a ball of cells right now) moves down the fallopian tubes and enters your uterus, where it attaches to the uterine wall. This is called implantation. After implantation, the developing placenta releases hCG into your bloodstream. Some hCG is also passed in your urine.
hCG Levels in Early Pregnancy
The initial level of hCG in your pregnant body will be low, but will progressively increase. In roughly 85 percent of healthy pregnancies, the levels of hCG will double every 30-72 hours. Between 7 and 12 weeks of pregnancy, hCG will start to peak, then decrease slightly. After 16 weeks pregnant, the level will remain relatively constant until you have your baby.
Try not to focus too much on hCG levels. They can vary widely between pregnancy to pregnancy, person to person. For example, some pregnant women have no measurable level of hCG on the day of their missed periods, while others have readings of 400 mIU/ml.
Overview of hCG Levels in Pregnancy
Below is a guide of normal hCG levels at different stages of pregnancy.
These numbers give a normal range. If your hCG readings fall outside of this guideline, try not to worry. It’s possible that your due date is off; you’re carrying twins or multiples; or that this pregnancy is just special.
If you’re worried, talk to your doctor about your hCG results. He or she should be able to reassure you that your baby is perfectly healthy.
- 3 Weeks (From Last Menstrual Period) – 0 to 50 mIU/ml
- 4 Weeks (From Last Menstrual Period) – 5 to 426 mIU/ml
- 5 Weeks (From Last Menstrual Period) – 18 to 7,340 mIU/ml
- 6 Weeks (From Last Menstrual Period) – 1080 to 56,500 mIU/ml
- 7-8 Weeks (From Last Menstrual Period) – 7,650 to 229,000 mIU/ml
- 9-12 Weeks (From Last Menstrual Period) – 25,700 to 288,000 mIU/ml
- 13-16 Weeks (From Last Menstrual Period) –13,300 to 253,000 mIU/ml
- Second Trimester – 4060 to 65,400 mIU/ml
- Third Trimester – 3640 to 117,000 mIU/ml
* hCG levels are measured using milli-international units per milliliter (mIU/ml).
Low hCG Levels in Pregnancy – Should You Be Worried?
If you have low hCG levels, you are naturally worried. There are a number of reasons why your hCG results are low, so you should discuss your worries with your doctor.
- Inaccurate Dates – Low hCG levels could mean that your due date was miscalculated. You’re not as far along as you originally thought.
- Ectopic Pregnancy – Unfortunately, low hCG levels may be a sign that you are having an ectopic pregnancy. When your fertilized egg implants outside of the uterus, like in the fallopian tube, less hCG is released.
- Miscarriage or Blighted Ovum – Sometimes, having low hCG levels may mean that your pregnancy isn’t healthy, and you could end up miscarrying.
- Your baby has died – hCG levels that continue to decline can mean that your baby has already passed away in the womb.
Keep in mind that many healthy pregnancies have low hCG levels, so low hCG results may not mean anything is wrong with your pregnancy.
If you get a low result, your doctor can recheck your hCG levels with a simple blood test within 2-3 days. If you’re ever worried about anything, please have a frank and open conversation with your healthcare provider about your concerns.
High hCG Levels and Pregnancy
On the other hand, if you get a high hCG level during pregnancy, it could mean any of the following:
- Multiple Pregnancy – Higher levels of hCG may mean that you’re having twins, triplets, or multiples.
- Molar Pregnancy – hCG levels that are high can be a sign that you have a molar pregnancy. So instead of having a growing baby inside of your womb, there’s a rare mass or growth that is growing instead.
- Choriocarcinoma – This is a fast-growing cancer that grows in a woman’s uterus. It occurs when cancerous cells start growing in the tissue that would have become the placenta. High hCG levels can be an indication that you don’t have a normal pregnancy.
If you get a high hCG result, your doctor will want to recheck your levels in a few days to evaluate any changes. If your healthcare provider believes that something is wrong, he or she will let you know.