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Pregnancy

Low hCG levels: Does it Always Mean a Miscarriage?

woman with low hcg levels

Essential Takeaways

  • Normal hCG levels vary significantly between women
  • Monitoring hCG levels can be a useful way to check your pregnancy is progressing normally
  • Low levels of hCG do not necessarily mean you are having a miscarriage

If you have been told you have low hCG levels you may be worried about what this means for your pregnancy. Normal hCG levels can vary enormously between women and low hCG levels are not always a cause for concern.

What is hCG?

hCG is a hormone produced by the cells of the placenta during pregnancy. After implantation of the embryo the placenta begins to produce increasing amounts of hCG. The hormone stimulates the production of progesterone by the corpus luteum to maintain the pregnancy. Pregnancy tests work by detecting the presence of hCG in your urine.

What are normal hCG levels in early pregnancy?

Normal levels of hCG vary widely between women. Women can even experience a considerable difference in hCG levels from one pregnancy to the next.

Low levels of hCG can be detected in your blood serum as soon as implantation is complete. As your pregnancy progresses the placenta grows in size leading to increasing levels of hCG.

The table below gives a guideline as to the normal range of hCG levels during each week of pregnancy. hCG levels are measured in milli-international units of hCG hormone per milliliter of blood (mIU/ml).

Pregnancy week

woman in bed

(weeks since last menstrual period)

Normal range for hCG (mIU/ml)
Non-pregnant 0 – 5
3 5 – 50
4 5 – 426
5 18 – 7340
6 1080 – 56 500
7 – 8 7650 – 229 000
9 – 12 25 700 – 288 000
13 – 16 13 300 – 254 000
17 – 24 4060 – 165 400
25 – 40 3640 – 117 000

Immediately after implantation hCG levels are very low. In a healthy pregnancy, levels of hCG double every 24 – 48 hours during the first three to five weeks. From weeks five to six the doubling time slows to 48 – 72 hours.

The rate of increase then slows further and hCG levels reach a peak of around 100,000 mIU/ml by week 10. After this hCG levels decrease and remain stable at approximately 20,000 mIU/ml for the remainder of pregnancy. The higher levels of hCG in the first trimester are the reason women often experience more intense pregnancy symptoms in early pregnancy.

It is important to consider the varying levels of hCG during pregnancy when taking a pregnancy test. Testing too early (before 12 days past ovulation) could mean that hCG levels are too low to be detected or result in a faint line on the pregnancy test. Testing later in pregnancy, however, can lead to a false negative result due to a phenomenon called the hook effect. 

Pregnancy tests work by detecting a specific type of hCG known as intact hCG. Later in pregnancy levels of another type of hCG called hCG-βcf can increase. hCG-βcf prevents the pregnancy test from detecting the original intact hCG resulting in a false negative result.

How is hCG measured?

hCG levels are not routinely tested during pregnancy. If your doctor has cause for concern monitoring hCG levels can be a useful way to check your pregnancy is progressing normally.

A single hCG test may be used to see if your levels are within the expected range for the stage of your pregnancy. Given the wide range of normal hCG values your doctor will often find it more useful to check the doubling time of your hCG levels. To do this serial hCG measurements will be made two to three days apart.

How common is low hCG in early pregnancy?

If your hCG levels are lower than expected, it is not necessarily a cause for concern. Your doctor will usually be more interested in the rate at which your hCG levels are rising.

A healthy pregnancy is usually based on an hCG increase of 66% or more over two days. It is worth keeping in mind that slow rising hCG levels occur in around 15% of pregnancies that continue without complications. One study has even shown that an hCG rise of at least 35% can still be considered normal.

What causes low hCG levels?

Miscalculated gestational age

A common reason for low hCG levels is a miscalculated gestational age. This happens when the stage of pregnancy and the estimated birth date are wrong.

Gestational age is calculated based on the date of your last menstrual period. If you have irregular cycles, long cycles with late ovulation, or cannot remember the exact dates of your last period, your hCG levels may appear lower than expected but in actual fact be normal for the stage of your pregnancy.

When calculating how many weeks pregnant you are it is in fact more accurate to date from time of ovulation. Implantation typically occurs between eight and 10 days post ovulation. Once implantation is complete levels of hCG begin to rise and can be detected using a pregnancy test by around 12 days post ovulation.

Ectopic pregnancy

hCG levels that are slow rising or level off before eight weeks can indicate an ectopic pregnancy. An ectopic pregnancy is an abnormal pregnancy where the embryo implants outside of the uterus, usually in the Fallopian tube.

It is important to remember that the rate of hCG increase varies widely between women. The rate of increase also slows towards the end of the first trimester. Because of this hCG measurements are used in combination with ultrasound to diagnose ectopic pregnancy.

Low hCG levels in miscarriage

Does low hCG mean miscarriage?

Miscarriage is a pregnancy loss before 20 weeks of gestation. Low hCG levels can sometimes indicate that you have had or will have a miscarriage. Normal levels of hCG vary between women and the stage of pregnancy however so low levels of hCG are not always a sign of miscarriage.

Does slow rising hCG mean miscarriage?

Like the level of hCG, the rate at which hCG levels rise differs significantly between women and the stage of pregnancy. Slower doubling times of hCG in the first trimester have been associated with an increased risk of miscarriage but studies have also shown that slow rising hCG levels occur in around 15% of healthy pregnancies.

Does falling hCG mean miscarriage?

Falling hCG levels can be a sign of a miscarriage. Falling levels of hCG will often be accompanied by additional symptoms such as bleeding or cramping. Further testing including an ultrasound scan will be required to check the health of your pregnancy.

Can you increase hCG?

Unfortunately, there is nothing that can be done to prevent or treat low hCG levels.

If the low levels are caused by a pregnancy loss or an ectopic pregnancy, treatment will be focused on ensuring any remaining pregnancy tissue is passed or removed from the body

It is important to remember that low hCG levels are not caused by anything you have done. If low hCG levels are due to a pregnancy loss this does not necessarily affect your chances of getting pregnant again.

 


View sources

Kadar N, Caldwell BV, Romero R, A method of screening for ectopic pregnancy and its indications, Obstetrics and gynecology, 1981

Morse CB, Sammel MD, Shaunik A, Allen-Taylor L, Oberfoell NL, Takacs P, Chung K, Barnhart KT, Performance of human chorionic gonadotropin curves in women at risk for ectopic pregnancy: exceptions to the rules, Fertility and sterility 2012

Elizabeth Oliver, PhD

Elizabeth Oliver is a researcher and freelance writer with a passion for reproductive health and endocrinology. She completed her masters in reproductive sciences at the University of Edinburgh and PhD in female reproductive biology at Imperial College London. She currently specializes in male fertility at the Karolinska Institutet Stockholm.

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