Lower than normal levels of hCG may indicate a problem with the pregnancy including:
- ectopic pregnancy
- fetal death
Levels of hCG can vary significantly between individuals and from one pregnancy to the next in the same person. But, typically, hCG levels follow a typical range throughout a healthy, uncomplicated pregnancy.
Low hCG levels in early or late pregnancy
Levels of hCG tend to decrease in the later stages of pregnancy.
Levels of hCG typically increase in the first trimester of a healthy pregnancy.
Levels of hCG usually increase during the first trimester, peak by weeks 8 to 11, and then decline to a steady level in the later stages of the pregnancy.
This means that as the pregnancy develops, hCG becomes less useful as a way to monitor it. When hCG levels do not increase or decrease as they should, it may be a sign of a problem with the pregnancy.
What are the causes?
Increasing levels of hCG usually mean that a pregnancy is healthy. However, low hCG levels are not always a sign that something is wrong.
Possible causes of low hCG levels are:
A blighted ovum occurs when a fertilized egg attaches to the wall of the uterus, but the embryo fails to develop.
This can happen during early pregnancy, sometimes before a person even knows they are pregnant.
Miscarriage is also known as spontaneous abortion and happens when the embryo dies naturally before 20 weeks of gestation.
Levels of hCG may rise initially in these situations but fail to increase or decrease as they should afterward.
Miscalculated gestational age
Levels of hCG may appear low if a doctor has miscalculated the baby's due date.
This happens when the stage of pregnancy and the estimated date of birth are wrong.
Calculating these events is based on the dates of a woman's last menstrual period, so miscalculations can occur if someone experiences irregular periods or is not sure when they had their last period.
Low levels of hCG can indicate whether a pregnancy is in a stage where low hCG levels are normal, such as in very early pregnancy, or in a pregnancy that is post-11 weeks.
Sometimes, in cases of miscalculated gestational age, the level of hCG may be lower than expected but not abnormal for the pregnancy.
This is an abnormal pregnancy where the embryo attaches outside of the uterus, usually inside the fallopian tube, the tube that carries the egg from the ovary to the uterus.
Symptoms can include abdominal pain and vaginal bleeding. An ectopic pregnancy can be a very serious, and even life-threatening, condition. Levels of hCG remain low during an ectopic pregnancy.
Low levels of hCG are not always a sign of a problem.
Unfortunately, there is no cure for situations where low hCG levels are a cause for concern.
However, treatment is available for the underlying conditions that cause low hCG levels, such as a miscarriage or an ectopic pregnancy.
In case of a miscarriage
Treatment may involve removing any pregnancy tissue that has been left inside the uterus and might include medication or a surgical procedure.
In case of an ectopic pregnancy, the doctor may also prescribe medications or surgery to remove the affected fallopian tube and the pregnancy itself.
What are the symptoms?
Low hCG levels that result from a miscarriage or an ectopic pregnancy are usually accompanied by abdominal pain, with or without vaginal bleeding.
There is currently no way to prevent low hCG levels or its associated complications, such as a blighted ovum, a miscarriage, or an ectopic pregnancy.
Outlook and takeaway
Low levels of hCG are not always a cause for concern. Levels of hCG can differ between individuals and between different pregnancies in the same person. Some people may naturally have lower levels of hCG than others.
Taking measurements of levels throughout the pregnancy can indicate if the pregnancy is developing as expected.
Even if a complication associated with low hCG levels occurs, such as a miscarriage or an ectopic pregnancy, this does not mean that someone will be unable to get pregnant again or that their fertility is compromised. A successful pregnancy is still possible with low hCG levels.