The human chorionic gonadotropin (hCG) hormone is a glycoprotein that is released by the embryo only after its attachment to the uterine lining of the woman when she is pregnant. This is the reason why it is commonly known as the pregnancy hormone, as it allows us to confirm whether pregnancy has actually occurred or not.
Definition and function
Human chorionic gonadotropin (hCG) is a hormone secreted by the placenta after embryo implantation. The function of this glycoprotein is to interact with the LHCG receptor of the ovary and promote the maintenance of the corpus luteum once the woman becomes pregnant.
The fact that hCG promotes the maintenance of the corpus luteum at the beginning of pregnancy allows it to secrete progesterone during the first trimester.
hCG is often referred to as the pregnancy hormone because women only produce it during pregnancy, particularly in the placenta by the syncytiotrophoblast. It can be produced artificially using recombinant DNA technology, though.
It can be measured by blood or urine tests, although the former are more sensitive than the latter. Concentrations of hCG are commonly reported using thousandth international units per milliliter (mIU/ml).
Human chorionic gonadotropin tests
Although it is commonly known as beta hCG, this hormone has two subunits:
- α-subunit (alpha)
- It can be found in other hormones secreted by the pituitary gland such as the thyroid-stimulating hormone (TSH) hormone, or follicle-stimulating hormone (FSH).
- β-subunit (beta)
- It is only present in this hormone, and for this reason is the subunit that can be detected by pregnancy tests.
Pregnancy tests are able to detect beta hCG levels in urine and blood. We can distinguish two ways of detecting this hormone:
- Quantitative hCG blood test
- Used to check the precise level of hCG in blood.
- Qualitative hCG blood test
- Used to just indicate the presence of hCG in urine or blood, without showing a precise value.
As for quantitative tests, there exist a series of values used as a reference to find out whether a woman is pregnant or not, and the number of weeks in case the test is positive. You can find them in the following section.
Beta hCG levels in pregnancy
hCG is detectable during the entire course of pregnancy, but the values keep on varying as the baby grows.
Since it kicks in, and throughout the first trimester of pregnancy, hCG levels rise until they peak and level off at week 12-14. By this time, they can reach up to 200,000 mIU/ml.
Below you will find the general hCG reference values in blood, which can help you estimate how many weeks pregnant you are since the date of your last menstrual period (LMP):
- 9-130 mIU/ml: 3-4 weeks LMP
- 75-2600 mIU/ml: 4-5 weeks LMP
- 850-20800 mIU/ml: 5-6 weeks LMP
- 4000-100200 mIU/ml: 6-7 weeks LMP
- 11500-289000 mIU/ml: 7–12 weeks LMP
- 18300-137000 mIU/ml: 12-16 weeks LMP
- 1400-53000 mIU/ml: 16–19 weeks LMP (2nd trimester)
- 940-60000 mIU/ml: 19-41 weeks LMP (3rd trimester)
It is important to keep in mind that these reference values are approximate, and they are different with each pregnancy. For this reason, we recommend that you keep close attention to the progress of hCG levels instead of the particular value at each point. In this sense, and as we explained earlier, its levels should double every two days on a general basis.
In the case of women undergoing IVF treatment, if the result of a beta-hCG test is 50 or above 13 days post egg retrieval, your doctor will schedule the first transvaginal ultrasound. This way, we can see the number of gestational sacs and their location within the womb. Should the beta-hCG level be lower than 50, you will be retested several times to monitor the progress of hCG levels and make sure that the pregnancy is developing as it should.
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How to read beta hCG results
Generally, in IVF treatments, women are recommended to wait for 10 to 15 days after ovum pick-up (OPU) to take a pregnancy test and get accurate results. This is the reason why this period of time is known as two-week wait, often abbreviated as 2WW.
If you have been trying to conceive naturally, testing for pregnancy after a missed period is what most women do on a regular basis.
Nevertheless, hCG start to be produced by the body after embryo implantation to the womb takes place, and increase its levels progressively up until the end of the first trimester, when they normally level off. hCG doubling time is usually between 48-72 hours, so we recommend that you repeat the test after a few days if you think the result was inaccurate.
The earlier a pregnancy test is done, the harder it will be for hCG levels to be detectable. Subsequently, the greater the chances of getting a false negative result.
A positive result of 5 mIU/ml or over is considered enough as to be detectable by a quantitative hCG blood test, although this is considered the lowest level. As a general rule, you should expect a level of around 50 mIU/ml if you take the test on day 13 post FET approximately.
If you got a positive but too low result, you should repeat the test within 48 hours to check whether hCG levels have doubled, thereby making sure that you are indeed pregnant and the pregnancy is progressing adequately.
If you opt for a home pregnancy test (HPT), you should know that they are less accurate that blood tests. They are able to detect concentrations of 25 to 50 mIU/ml or over, depending on the provider.
We always recommend that you opt for quantitative hCG blood tests, as they are able to detect lower concentrations, with the precise value of the hormone in that moment.
Pregnancy test errors
Sometimes, pregnancy tests can fail and lead to errors, often referred to as false negative or false positive depending on the case.
Pregnancy tests can fail in the following situations:
- False positive
- When undergoing fertility treatment, it is common for patients to administer hCG injections to induce ovulation. As a consequence it can last in the body a few days, and lead to pregnancy test errors. In this case, the woman would get a positive result, when she is actually not pregnant. In natural pregnancies, it is very uncommon to get a false positive result, as no exogenous hCG administration is necessary. One can get a false positive result in cases of ectopic pregnancy, tumous, carcinomas…
- False negative
- Both in natural pregnancies and IVF pregnancies, if the test is done too early, you are at risk of getting a false negative result due to the levels of hCG still being too low. The only solution before a false negative is to repeat it within a few days.
What do abnormal hCG results mean?
When a woman gets herself tested for pregnancy, she can come across an abnormal result that is above or below what is considered normal. If the deviation is not so substantial, one should not be concerned. As we explained above, beta hCG levels are not the result of a mathematical equation, and therefore vary greatly from woman to woman.
However, if the deviation is considerably significant, it can be caused by any of the following situations:
- Results above average
- They may indicate multiple pregnancy, uterine choriocarcinoma, molar pregnancy (a.k.a. hydatidiform mole), some type of cancer or an abnormal cell proliferation.
- Results below average
- They may indicate a stillbirth, incomplete abortion, threatened miscarriage, ectopic pregnancy, etc.
FAQs from users
When is hCG produced after conception?
hCG is rapidly secreted after embryo implantation, which takes place around 6 days after conception. Once it kicks in, hCG levels double every two or three days. As explained above, it can be detected by a blood test about 11 days after conception, and 12-14 days if you use a HPT.
When do hCG levels stop doubling?
Usually, hCG levels off at 6,000 mIU/ml. From this moment on, it is expected to double every four days (keep in mind that, at the beginning, it doubles every 48 hours). The production of hCG is expected to stop rising around week 8-11 of pregnancy.
Some experts believe that the reason why hCG levels stop rising at this point is because the placenta starts making estrogen and progesterone from this moment on. In other words, that hCG is no longer necessary to stimulate the ovary, which was responsible for the secretion of these hormones up until that point.
How do pregnancy tests detect hCG?
Chemical tests for pregnancy, as you can read above, look for the presence of the beta subunit of hCG (human chorionic gonadotropin) in the urine or blood.
Most home pregnancy tests, which detect hCG in urine, are based on what is known as lateral-flow technology. This type of tests (lateral flow tests or lateral flow immunochromatographic assays) work by detecting the presence or absence of a target analyte in a sample.
Lateral-flow technology is based on the use of capillary beds, e.g. microstructured or sintered polymer, or pieces of porous paper, which are able to transport fluid rapidly.
Are hCG levels higher with twins?
Yes, hCG levels are indeed higher when a woman is pregnant with multiples. If you take a test too early and get a positive result, it might be a clue that you are having twins, but it should be clear that it does not mean that you are having twins by default. Sometimes, being able to get a positive so early can be due to a simply normal fluctuation in hormone production.
Can hCG levels go up and down?
Yes, as stated earlier, levels of hCG rise quickly at the beginning (and throughout the first trimester), and peak at 8-11 weeks, when they normally stop increasing and begin to fall.
On the other hand, hCG levels can fluctuate during the day, being higher in the morning simply because that is when the urine is most concentrated, and that is the reason why you are recommended to take a HPT in the morning. Some women have more concentrated urine in the afternoon or even in the evening. All in all, it varies from pregnancy to pregnancy.
When does hCG show in urine?
The sensitivity of home pregnancy tests is lower than blood pregnancy tests. HPTs can usually detect pregnancy 6-7 days after embryo implantation. In certain cases, it can be detected as early as 2 to 3 days before you miss your period, though rarely.
However, this is variable and in fact can lead to false negatives if the test is taken too early. If your body has not started producing hCG yet, you may get a false negative result.
When do hCG levels drop after miscarriage?
It can take four to six weeks after a miscarriage or abortion for hCG levels to drop to zero. Keep in mind that, if you miscarry or abort around the 8th to the 10th week of pregnancy, the level of hCG is at its highest at that point, so it will take time for it to drop below 5 mIU/ml.
Can you have normal hCG levels and still have twins?
In some singleton pregnancies, women have lower than normal hCG levels throughout the course of the pregnancy without it being a reason to be concerned.
This applies to some multiple pregnancies as well: even though hCG levels will be higher than with a single baby, they will be high but not so significantly as typically in multiple pregnancies. The levels of the pregnancy hormone vary greatly from woman to woman, so answering this question accurately is difficult.
Can hCG levels go up with a blighted ovum?
Yes, because the placenta produces hCG after embryo implantation. With a blighted ovum, even though there is no embryo, the placental tissue can remain in the body for a brief time and continue releasing hCG. They will stop doubling and begin to drop eventually, though.
When do hCG levels drop after giving birth?
Although, again, it varies from woman to woman, they usually disappear entirely throughout the 3rd week postpartum.
If hCG levels continue being present beyond this time, it may indicate the presence of placental tissue in the womb, a condition that can lead to late postpartum hemorrhage. The most severe cases can be treated by curettage.
Can hCG determine gender?
Some studies have shown that hormone concentrations in pregnancy can vary according to the gender of the baby, and that hCG levels are higher with a girl. Some researchers have even related severe morning sickness to the baby being a female fetus.
Other studies, however, only report this in later pregnancy. The truth is, the extent to which the maternal hormone levels can be related to the gender of the baby is very difficult to predict.
Can high hCG levels mean Down syndrome?
Yes, high hCG levels can be a concerning issue and translate into the presence of genetic alterations in the fetus, including Down’s syndrome, which can be evaluated along with other hormones with a triple marker screen test.
Suggested for you
If you have just taken a pregnancy test and got a positive result, you may be noticing some of the earliest pregnancy symptoms due to the changes that are now occurring in your body, including a rise in hCG levels. Learn more about them here: What are the first signs and symptoms of embryo implantation?
Some women think they are having the typical pregnancy symptoms without even being pregnant. If this is your case, you can find out why a woman can feel pregnant without even being so here: Pregnancy symptoms but negative test, what else could it be?