HCG Pregnancy Testing: Everything You Want To Know

What is HCG and Beta HCG

HCG (Human Chorionic Gonadotropin) is a hormone that is produced by the placenta, after the implantation of the embryo. It is often measured in order to determine if a woman is pregnant or not. Its main purpose during pregnancy is to signal the corpus luteum (the structure on the ovary that produces progesterone) and keep it from disintegrating at the end of the menstrual cycle. Without HCG and without a corpus luteum producing progesterone, the uterine lining would shed and you would get your period instead. This is why HCG is essential in maintaining the pregnancy during the first trimester, until the placenta is mature enough to produce progesterone on its own.

Extremely rarely, HCG can also be secreted by something other than a pregnancy, such as a tumor for example, however in the vast majority of cases, a positive HCG test in a woman means pregnancy.

The intact HCG molecule is made of two subunits, an alpha subunit, which is virtually identical to the subunits of other hormones in the body, like LH (Luteinizing Hormone) and TSH (Thyroid Stimulating Hormone) and a beta subunit, which is unique to HCG and is frequently measured to diagnose and monitor a pregnancy.

Apart from the intact HCG molecule, there are other HCG-related molecules that have a role in pregnancy (and occasionally in other conditions), such as the free beta subunit, hyperglycosylated HCG and pituitary HCG. They are not routinely tested for when monitoring a pregnancy, however.

Home pregnancy tests (HPTs)

The most well-known and widely used HCG testing available are the home pregnancy tests (HPTs). They are available in a variety of places, from doctor’s offices to drugstores and supermarkets and are produced by a wide variety of brands.

HPTs are self-diagnostic tools designed to detect Beta HCG in the urine and help women quickly determine if they are pregnant. HCG can start being excreted in the urine as early as 7 days after conception, but because most home pregnancy tests are not sensitive enough to detect very small amounts of Beta HCG, they have a better accuracy rate beginning about 14 days after ovulation/conception (or the first day of your missed period). Early Detection home pregnancy tests are available in some countries with HCG detection thresholds as low as 10mIU/ml, which is sensitive enough to offer a high accuracy reading even before the first day of your missed period.

This following table adapted from a medical study will give you a better picture of the average HCG concentration in urine during each day of early pregnancy. Keep in mind that typical Early Detection HPTs have a detection threshold of 10-25 mIU/ml, while normal HPTs have detection thresholds of 30-100 mIU/ml.

Days Post Ovulation/Conception	Median HCG concentration in urine (mIU/ml)	Normal range of HCG concentration in urine (mIU/ml)
7	0	0 - 0
8	0	0 - 2
9	4	0 - 11
10	12	3 - 27
11	25	9 - 57
12	48	15 - 94
13	75	29 - 196
14	137	45 - 301

In light of this evidence, the best time to get a confidently accurate result is at least 14 days post ovulation when using a regular HPT and at least 12 days post ovulation if using an Early Detection HPT. Of course, you can always test earlier than that, but even so, remember that testing any earlier than 9 days post ovulation will almost always give you a negative result, whether you have conceived or not.

It is generally recommended to take a pregnancy test first thing in the morning, when the urine is likely to be more concentrated. However you can also take the test during the day, ideally after taking some steps to help your urine become more concentrated, particularly if you are testing early.

Sometimes, even the best of HPTs may give a false negative or false positive reading.

A false negative reading means you are actually pregnant but the test gives you a negative result. This usually happens when:

The test was taken too early and the HCG concentration in the urine didn’t have time to build up to a detectable level
The test didn’t work properly (malfunctioned)
The urine is too diluted
The pregnancy is too advanced. Testing after the first 5-8 weeks of pregnancy may give a false negative reading, due to other unreadable HCG components crowding the antibodies on the HPT’s sensor strip. This is called a ‘hook effect’.
An ectopic pregnancy can sometimes cause HCG levels to fluctuate and become undetectable on occasion

A false positive result happens when you are not in fact pregnant, but the test is positive. This can happen when:

The test didn’t work properly (malfunctioned)
You saw evaporation lines. When you read the test after the recommended time frame, occasionally a vague second line may appear after the urine has evaporated off the test
You were previously injected with HCG during a fertility procedure (HCG injections are sometimes used to trigger ovulation). The HCG from the injection takes time to leave your body, so wait at least 2 weeks before taking a pregnancy test.
You recently suffered a pregnancy loss. Depending on how advanced the pregnancy was, the HCG in the body can take anywhere between 2 and 8 weeks to return to undetectable levels.
A medical condition is causing the false positive reading, including kidney disease, pituitary dysfunction, Inflammatory Bowel Disease, ulcers, HCG-secreting tumor, etc.
You are taking certain medications which could make it more likely to obtain a false positive result on a home pregnancy test. Examples include certain antipsychotics and anti-anxiety medications, bromocriptine, antihistamines and others.

Blood HCG testing

A serum HCG test is highly accurate at determining the amount of HCG in your blood. It is sensitive to even very small amounts of circulating HCG.

Often, multiple testing choices are made available by various laboratories, including HCG, Total HCG, Beta HCG, Total Beta HCG, Free Beta HCG. To confirm and monitor pregnancy, we are interested in either the (Total) HCG or the Beta HCG test.

HCG in the blood is measured in mIU/ml and normally a value lower than 5mIU/ml is considered negative for pregnancy, while a value higher than 20mIU/ml is considered positive. A result between 5-20mIU/ml is suggestive of very early pregnancy but you will need further testing to confirm it.

Even the most precise of blood tests are still not 100% accurate. Sometimes, a false negative result can happen when:

The test was taken too early, earlier than 7 days post conception
There was a laboratory error or mistake

Similarly to a HPT, the HCG blood test can yield a false positive result in these cases:

There was a laboratory error or mistake
You were previously injected with HCG during a fertility procedure (HCG injections are sometimes used to trigger ovulation). The HCG from the injection takes time to leave your blood, so wait at least 2 weeks before taking a pregnancy test.
You recently suffered a pregnancy loss. Depending on how advanced the pregnancy was, the HCG in the body can take anywhere between 2 and 8 weeks to return to pre-pregancy levels.
A medical condition is causing the false positive reading, including kidney disease, pituitary dysfunction, Inflammatory Bowel Disease, ulcers, HCG-secreting tumor, etc.
You are taking certain medications which could make it more likely to obtain a false positive result on the HCG test. Examples include certain antipsychotics and anti-anxiety medications, bromocriptine, antihistamines and others.

The earliest time to first take a blood pregnancy test is starting around 8-9 days post ovulation/conception.

Normal HCG levels during pregnancy

HCG values during each week of pregnancy can vary greatly from one woman to the next. The table below gives you some orientative ranges of what is normal for each week:

Weeks of pregnancy (calculated from LMP)	Blood HCG median value (mIU/ml)	Blood HCG normal range (mIU/ml)
3 weeks	17.5	6 - 72
4 weeks	141	10 - 700
5 weeks	1400	217 - 7140
6 weeks	3340	160 - 31.000
7 weeks	39.700	3.700 - 163.500
8 weeks	90.000	32.000 - 150.000
9 weeks	106.000	63.800 - 160.000
10 weeks	85.000	46.000 - 200.000
12 weeks	67.0000	28.000 - 210.000
14 weeks	34.400	14.000 - 62.000

The above values can be even greater if you’re expecting twins or multiples!

HCG levels rise very quickly during the first weeks of pregnancy, reaching a maximum around weeks 9-12, after which they begin to drop. They keep at a low level for the remainder of the pregnancy but never fall below 5 mIU/ml (pre-pregnancy value) until after delivery.

During early pregnancy, HCG levels are expected to double every 48 hours between weeks 2 and 6 (as calculated from the last menstrual period). After week 7, a doubling time of 36-72 hours is also considered normal.

To check whether your early pregnancy is progressing normally, the doctor will sometimes order serial HCG testing every 2 days. Ideally, the values will double during this time. If they do not double, a minimum increase of at least 35% is expected, anything less than that being suggestive of a miscarriage or an ectopic pregnancy. Here is a very useful doubling time calculator if you want to check whether your HCG levels are rising as they should: http://perinatology.com/calculators/betahCG.htm.

Before a miscarriage, the HCG levels will usually stop rising or they will rise very slowly. After a miscarriage, the HCG levels are expected to fall by 50% every 48-36 hours until they finally reach a level of below 5 mIU/ml. If they don’t fall below this value, it can mean that some tissue from the pregnancy is still retained in the body and this could require a D&C (dilation & curettage) to properly clean the uterus.

When HCG levels are fluctuating (going up, then down, then up again), it is indicative of an ectopic pregnancy and special attention should be paid to locating the pregnancy on the ultrasound. A growing ectopic pregnancy can be a dangerous thing and lead to the rupture and loss of the fallopian tube, internal bleeding and emergency surgery. However, if discovered early, it can be treated by medication alone. HCG levels will continue to be monitored throughout the treatment, to make sure they fall back below 5 mIU/ml.

HCG levels and ultrasound findings

Both HCG testing and transvaginal ultrasound are key diagnosis tools when it comes to detecting and evaluating pregnancy. When their results are correlated, they can determine with great accuracy whether the pregnancy is developing normally, failing or is located outside the uterus (ectopic/extrauterine).

Normally, a gestational sac should be visible on transvaginal ultrasound (TVU) when HCG levels reach 1000-2000 mIU/ml (around weeks 5-6 of pregnancy). An empty uterus when HCG levels are above 3000 mIU/ml is highly suggestive of ectopic pregnancy, although even in this case there is a small 0.5% chance that the pregnancy is actually inside the uterus.

On transabdominal ultrasound, the gestational sac becomes visible a bit later, when the HCG levels exceed 6000 mIU/ml, typically around 7 weeks

The yolk sac can be first distinguished on TVU once the HCG levels approach 8000 mIU/ml (week 6-7). If the levels exceed 15,000 mIU/ml and no yolk sac is visible, it can mean a problem with the pregnancy, such as a blighted ovum.

The fetal pole and heart tone become measurable about the time HCG titers reach 10,000 mIU/ml, which corresponds with pregnancy weeks 7-8. If HCG levels are higher than 40,000 mIU/ml and no fetal pole or heart rate can be detected, it could mean the pregnancy is failing.