HCG levels in pregnancy

What is hCG?

HCG is a hormone produced during pregnancy. The letters stand for human Chorionic Gonadotropin. After an egg is fertilized and implants in the uterus, the cells that will eventually form the placenta start making hCG.

HCG is often the first indicator of pregnancy. The hormone can be detected through a blood test about 11 days after conception. However, most women first discover they're pregnant using a store-bought home pregnancy test, which measures hCG levels in the urine.

HCG is detectable in urine at around 12 to 14 days after conception, when you're around 4 weeks pregnant. (The most common way to calculate your pregnancy due date is from the first day of your last menstrual period, which is typically two weeks before conception.)

If you think you're pregnant but have a negative pregnancy test, it may be that you took the test too early, or that your urine is very diluted. Rest assured that you will have hCG in your blood and urine if you're pregnant. You may want to take the test again in another day or two – first thing in the morning, when your urine is more concentrated, is best.

In early pregnancy, hCG levels typically double about every two to three days. Levels generally peak at around 8 to 14 weeks after conception. After that they decline somewhat, and usually plateau during the second and third trimester.

It is possible – though uncommon – for hCG levels to fall instead of rise, and then rise again. While declining levels often signal a miscarriage, sometimes the levels go back up and the pregnancy proceeds normally.

What hCG levels mean in pregnancy

Your hCG levels at any particular point in time during pregnancy don't mean much. Although there are average ranges of hCG levels for different stages of pregnancy, these can vary dramatically from woman to woman, and from pregnancy to pregnancy. Even if your hCG levels are outside the "normal" range, you can still have a perfectly healthy pregnancy and baby.

That said, it is important that your hCG levels increase during early pregnancy. If your hCG levels don't continue to rise rapidly during the first few weeks or if they start to drop, this can signal a problem such as an ectopic pregnancy or miscarriage. Higher-than-typical hCG levels can signal that you're carrying multiples or, in rare cases, have a molar pregnancy.

Often, you won't know what your hCG levels are during pregnancy. Home pregnancy tests don't give a specific hCG number. However, you may learn your hCG levels if your provider orders a blood test to confirm your pregnancy or as part of a screening test.

Your provider may also order a series of two or more hCG blood tests if they have concerns about how your pregnancy is progressing. These blood tests, taken two to three days apart, can tell your provider whether your hCG levels are trending in the right direction.

Causes of low hCG levels

Low hCG levels in pregnancy can be a sign of the following:

• Your due date was miscalculated. Providers typically calculate your baby's gestational age and your due date based on the date of your last period. But it's common to get this calculation wrong, especially if you have irregular periods or don't remember the date of your last period. Your hCG levels may be lower than expected because your pregnancy isn't as far along as your provider thought.
• Miscarriage. If your hCG levels don't go up during early pregnancy or if they start to decline, this could signal you've had or are about to have a miscarriage. If this is the case, you may experience other signs of miscarriage, such as bleeding and abdominal pain.
• Blighted ovum. This is when a fertilized egg implants in the uterus but never develops into an embryo, so the hCG levels don't rise. It's a common cause of miscarriage during early pregnancy.
• Ectopic pregnancy. This is a rare but dangerous condition in which the fertilized egg implants in the fallopian tube instead of the uterus. It's usually accompanied by symptoms such as pelvic pain and vaginal spotting.

HCG chart: hCG levels by week

While hCG levels can vary widely from person to person and from pregnancy to pregnancy, they tend to fall within a range. Below is the average hCG range during pregnancy, based on the number of weeks since your last menstrual period (Note, if your cycle is irregular, these numbers may not apply).

HCG is measured by milli-international units of hCG hormone per milliliter of blood (mIU/ml).

Learn more:

11 early pregnancy symptoms

All about home pregnancy tests