What is an hCG test?
Human chorionic gonadotropin (hCG) is a hormone produced by your placenta once an embryo implants in the uterus.
The purpose of the hormone is to tell your body to continue to produce progesterone, which prevents menstruation from occurring. This protects the endometrial uterine lining and your pregnancy.
A pregnancy test can detect hCG in your urine if your levels are high enough. This is how the test identifies that you are pregnant. But only a blood test can give you a precise numerical hCG reading.
Standard hCG levels
Standard hCG levels vary quite massively from woman to woman. This is because hCG levels really depend on what is normal for you, how your body responds to pregnancy, as well as how many embryos you are carrying. The way a woman’s body reacts to pregnancy is entirely unique.
The table below gives you a guideline as to the normal wide range of hCG levels in each week of pregnancy. hCG levels are measured in milli-international units of hCG hormone per milliliter of blood (mIU/mL).
|Pregnancy week||Standard hCG range|
|3 weeks||5–50 mIU/mL|
|4 weeks||5–426 mIU/mL|
|5 weeks||18–7,340 mIU/mL|
|6 weeks||1,080–56,500 mIU/mL|
|7–8 weeks||7,650–229,000 mIU/mL|
|9–12 weeks||25,700–288,000 mIU/mL|
|13–16 weeks||13,300–254,000 mIU/mL|
|17–24 weeks||4,060–165,400 mIU/mL|
|25–40 weeks||3,640–117,000 mIU/mL|
hCG levels usually consistently rise until around week 10–12 of your pregnancy, when the levels plateau or even decrease. This is the reason why pregnancy symptoms can be greater in the first trimester and ease off after this time for many women.
In early pregnancy, hCG levels usually double every two to three days. Interestingly, when the measurements start off high they don’t expand at the same rate. If they start off more slowly, the increase ends up happening much quicker.
If your hCG levels fall below the normal range, your doctor may want you to have a blood test every two to three days to ensure the levels are increasing. A single measurement of your hCG level is not useful. To give an accurate indication, a series of hCG blood tests needs to be taken a couple of days apart and the readings compared. There is often variation with a rapid increase in numbers, especially in the first few weeks of pregnancy.
Causes of low hCG levels
If your hCG levels fall below the normal range, it’s not necessarily a cause for concern. Many women have gone on to have healthy pregnancies and babies with low hCG levels. Most women don’t ever have cause to find out what their hCG levels are specifically.
However, sometimes low hCG levels can be caused by an underlying problem.
Gestational age miscalculated
Typically, the gestational age of your baby is calculated by the date of your last menstruation. This can be easily miscalculated, particularly if you have a history of irregular periods or are unsure of your dates.
When low hCG levels are detected, it’s often because a pregnancy that was thought to be between 6 and 12 weeks is actually not that far along. An ultrasound and further hCG tests can be used to calculate the gestational age correctly. This is usually the first step when low hCG levels are detected.
A miscarriage is a pregnancy loss that occurs before 20 weeks of gestation. Sometimes low hCG levels can indicate that you have had or will have a miscarriage. If the pregnancy fails to develop a placenta, then the levels may be normal initially but fail to rise. Common signs that you are experiencing a miscarriage are:
- vaginal bleeding
- abdominal cramps
- passing tissue or clots
- cessation of pregnancy symptoms
- discharge of white/pink mucus
This is when an egg is fertilized and attaches to the wall of your womb, but does not continue to develop. When the gestational sac develops, hCG hormone can be released, but the level does not rise since the egg doesn’t develop.
This occurs very early in pregnancy. Most women won’t even know that it’s taken place. Usually you’ll experience your normal menstruation symptoms and assume it’s your usual period. However, if you’re trying to conceive, you may do an early pregnancy test that could pick up the presence of hCG.
An ectopic pregnancy is when the fertilized egg remains in the fallopian tube and continues to develop. It’s a dangerous and life-threatening condition, as it may cause the fallopian tube to rupture and bleed excessively. Low hCG levels can help to indicate an ectopic pregnancy. At first the symptoms of an ectopic pregnancy can be similar to those of a normal pregnancy, but as it progresses you can experience the following:
- abdominal or pelvic pain that worsens with straining or movement (this can happen strongly on one side initially and then spread)
- heavy vaginal bleeding
- shoulder pain caused by internal bleeding (the bleeding aggravates the diaphragm and presents as pain at the tip of the shoulder)
- pain during intercourse
- pain during a pelvic examination
- dizziness or fainting due to internal bleeding
- symptoms of shock
How is it treated?
Unfortunately, there is nothing that can be done to treat low hCG levels, though low levels alone are not always a cause for concern.
If your low hCG levels have been caused by a miscarriage, it’s possible that you may need treatment if any pregnancy tissue is left inside your womb. If there’s no tissue retained, then you won’t require any treatment at all. If there is, then there are three treatment options available:
- You can wait for the tissue to pass naturally.
- You can take medication to help you to pass the tissue.
- You can have it surgically removed.
Your doctor will discuss with you what the best course of action is.
The treatments for an ectopic pregnancy are similar. Medications are given to prevent the pregnancy from continuing to grow. If surgery is required, it’s standard for the doctors to remove the affected fallopian tube as well as the pregnancy.
What’s the outlook?
Low hCG levels alone are not necessarily a reason to be worried. There are many factors that affect the levels, and the normal range varies hugely between individual women. Your doctor will be able to monitor your hCG levels for you if you have concerns. Even if they remain low, there is nothing that you can do. It’s also important to remember that low hCG isn’t caused by anything you’ve done.
If your low hCG levels are due to a pregnancy loss, this doesn’t necessarily mean that you won’t be able to get pregnant and carry to term in the future. If you lose a fallopian tube due to an ectopic pregnancy, your fertility shouldn’t change significantly as long as your other tube is functioning. Even if it isn’t, reproductive technologies like in vitro fertilization can help lead to successful pregnancy.