HCG levels in pregnancy: what you should know

Knowledge from midwifery practice

HCG is an important hormone in early pregnancy. Rising HCG levels are an indicator of successful pregnancy. For instance, pregnancy tests work by detecting HCG.

In some cases, a blood sample is taken to determine the exact HCG level which is then checked again after a few days. For example, this is done if it is not possible to detect an embryo in the uterus. In such cases, regular check-ups are recommended until it is certain that there is a pregnancy.

Ann-Katrin Hiller

Your midwife from Livella

It’s not uncommon for a woman’s hormones to go crazy during pregnancy. But even though they can cause quite some issues, they also play an important role for the normal development of a pregnancy.

One of these hormones is the so-called HCG. The body starts producing HCG as soon as the fertilised egg has implanted into the uterus. Pregnancy tests detect HCG in a woman’s urine. A positive test indicates a pregnancy.

In addition, the pregnancy hormone also plays a crucial role for maintaining the pregnancy. Read on to learn more about the importance of HCG and what information can be gained from monitoring HCG levels in pregnancy.

Table of content

What is HCG and what is its role in pregnancy?

What do HCG levels in pregnancy indicate?

What does it mean if HCG levels in pregnancy are too high or too low?

What are normal HCG levels in pregnancy?

HCG levels in pregnancy: how do pregnancy tests work?

Other reasons for monitoring HCG levels in pregnancy

HCG levels in pregnancy: key facts at a glance

What is HCG and what is its role in pregnancy?

HCG (sometimes also called beta HCG) is short for “Human Chorionic Gonadotropin”. Commonly referred to as pregnancy hormone, its levels rise constantly in the first weeks of pregnancy. The rise in the woman’s HCG levels is detected by pregnancy blood or urine tests and hence delivers the first indication that there is a pregnancy.

As soon as the fertilised egg has implanted into the uterus, the cells of the developing embryo start producing HCG and simultaneously form the placenta which then takes over the production of HCG. The HCG is released into the mother's bloodstream through which it is transported to the ovaries where it stimulates the production of oestrogen and progesterone in the corpus luteum (also known as yellow body).

HCG is hence crucial for maintaining the pregnancy. That’s because oestrogen and progesterone are responsible for placenta growth and further prevent the onset of menstruation, which would mean the end of the pregnancy.

Good to know: Rising HCG levels almost always indicate pregnancy. It’s only in rare cases that high HCG levels are the result of a tumour which can also produce HCG.

HCG is essential in early pregnancy because it helps the body establish the pregnancy successfully. In a normal pregnancy, HCG levels increase continually starting from the moment where the fertilised egg implants into the uterus wall.

HCG levels in pregnancy start decreasing as soon as the oestrogen and progesterone production is taken over by the placenta because the pregnancy hormone is then no longer needed to stimulate the yellow body.

In short, the pregnancy hormone HCG not only indicates pregnancy, but it also plays a crucial role in maintaining the pregnancy during the first trimester.

What do HCG levels in pregnancy indicate?

The importance of HCG levels in pregnancy is twofold. For one thing, elevated HCG levels indicate pregnancy because pregnancy tests are designed to detect the pregnancy hormone in a woman’s blood or urine (more on this later).

For another, increasing HCG levels in the first few weeks indicate that the woman has a continuing pregnancy. By monitoring HCG levels, health professionals can check if the pregnancy is developing normally. If HCG levels are too high or too low, this could be a sign that there is more than one pregnancy or that the mother is about to suffer a miscarriage.

What does it mean if HCG levels in pregnancy are too high or too low?

HCG levels in pregnancy are an important indicator of normal pregnancy development. Low or elevated HCG levels can indicate problems.

Low levels of HCG can indicate:

failed implantation of the fertilised egg
pending miscarriage
ectopic pregnancy (i.e. pregnancy lodged outside the womb, typically in the fallopian tube)

Unusually high HCG levels, on the other hand, can indicate:

a molar pregnancy (i.e. abnormal development of baby and placenta)
a multiple pregnancy
a placental tumour which has developed from the cells that form the placenta
the formation of another malignant tumour in the mother’s body which produces HCG

However, it is important to remember that high or low HCG levels can have many different causes and are not necessarily a cause for concern or worry. For instance, low HCG levels could be due to an error in the calculation of the mother’s gestational age. As long as HCG levels in pregnancy are continually rising, there is usually no reason to worry.

What are normal HCG levels in pregnancy?

HCG levels of non-pregnant women are typically below 4 IU/L (international units per litre). If the fertilised egg has successfully implanted into the uterus, HCG levels quickly start to rise and continue increasing throughout the whole of the first trimester.

During the first week after conception, serum HCG levels are typically between 5 and 50 IU/L. In the second week, they are usually somewhere between 50 and 500 IU/L. A good rule of thumb is that HCG levels double roughly every two days in the first weeks of pregnancy. Thereafter, it slows down.

But when are HCG levels in pregnancy at their highest? HCG levels are highest towards the end of the first trimester, i.e. around week 12. After that, HCG levels start decreasing.

This is because the production of oestrogen and progesterone is taken over by the placenta from week 13 onwards. As a result, the pregnancy hormone HCG is no longer needed to stimulate hormone production in the corpus luteum.

HCG levels in pregnancy: how do pregnancy tests work?

Pregnancy tests which are available in pharmacies and health stores detect HCG in the mother’s urine. Since the body starts producing HCG as soon as the fertilised egg has implanted into the uterus, the pregnancy hormone can be detected at quite an early stage in pregnancy.

Blood tests can detect an existing pregnancy about six to nine days after conception. However urine tests take a little longer to detect HCG so that they should be done a little later to get reliable results. It roughly takes one week longer for urine HCG levels to be high enough for a reliable test result.

To be on the safe side, a pregnancy test should only be taken after the first day of a missed period because this is when HCG levels in urine are typically high enough to be detected by the test. Ideally, the test should be done early in the morning with the first pee of the day since that’s when HCG concentration is highest.

Early pregnancy tests which can already detect a pregnancy before a missed period are less reliable. If an early pregnancy test gives a negative result, it is best to repeat the test at a later point to be on the safe side.

Ultrasound scans can typically detect a pregnancy in the womb around six weeks after the last period. Health professionals can use ultrasound to determine how far along the mother is. Once it is clear how many weeks pregnant she is, the next step is to create a schedule for the different antenatal care appointments.

Other reasons for monitoring HCG levels in pregnancy

HCG levels in pregnancy mainly fulfil two purposes. For one thing, measuring HCG levels can show whether a woman is pregnant or not. For another, monitoring HCG levels allows health professionals to check whether the pregnancy is developing normally.

The latter is particularly important in the case of intrauterine insemination where HCG levels are checked to see if the procedure was successful and if there really is a pregnancy. HCG levels that deviate from the norm can further be a sign of an ectopic or multiple pregnancy.

However, HCG levels play yet another important role in pregnancy. In fact, maternal HCG levels are also measured when screening for chromosomal disorders in the baby. The so-called combined test also includes a blood test in pregnancy which tests for PAPP-A and HCG. Based on the results of the blood test and the nuchal translucency scan, health professionals can calculate the chance of the baby having a chromosomal condition.

Good to know: The pregnancy hormone HCG is also associated with many of the typical side effects of pregnancy, including morning sickness and dizziness.

HCG levels in pregnancy: key facts at a glance

HCG stands for “Human chorionic gonadotropin". It is a hormone which is produced by the placenta during pregnancy.
The pregnancy hormone can be detected in the mother’s blood and urine shortly after successful implantation of the fertilised egg into the uterus, which is how commercially available pregnancy tests work.
Thereafter, HCG levels can be monitored to check that the pregnancy is developing normally.
During the first few weeks of pregnancy, the mother’s HCG levels increase continually. This stimulates the production of oestrogen and progesterone in the corpus luteum.
As soon as the placenta takes over the production of progesterone, HCG levels begin to drop.
In addition to stimulating progesterone production, the pregnancy hormone serves as an indicator for successful intrauterine insemination and the normal development of a pregnancy.