Pregnancy Test hCG (Human Chorionic Gonadotropin)

What is human chorionic gonadotropin (hCG)?

hCG (Human Chorionic Gonadotropin) often called the pregnancy hormone is a hormone that is only produced by the placenta during pregnancy.

The fertilization of the woman's egg by the man's sperm takes place in the woman's tubes, and as a result of fertilization, an embryo is formed. In the outer layer of the embryo, trophoblastic cells develop, which enable the embryo to attach to the uterine wall. These trophoblastic cells secrete the hCG hormone called Human Chorionic Gonadotropin hormone. The unique role of hCG is to support pregnancy.

Within 5 to 6 days after fertilization, the embryo settles in the inner layer of the uterus and starts to secrete more and more hCG hormone. hCG is found in urine or blood around 10 to 11 days after conception (when a sperm fertilizes an egg). It takes slightly longer for hCG to register on urine tests.

Women cannot understand this process because the expected menstrual date has not come yet. Although secreted hCG is found in blood and urine, measurements done before the expected period day cannot show whether the pregnancy is present or not.

If there is a delay in the expected period, the hCG hormone can be measured in the blood or urine to determine whether there is a pregnancy or not. Tests performed before the expected period do not give accurate information, the hCG test has nothing to do with ovulation tests, ovulation tests can only give information about the day of ovulation and do not show whether there is pregnancy or not.

Tests performed earlier than the calculated date or incorrect calculation of the last menstrual period may result in low or negative tests. For this reason, in doubtful cases, the test should be repeated after a few days.

What is the role of hCG?

The hCG hormone plays a vital role in early pregnancy as it helps the corpus luteum, and helps maintain the uterus lining. Since this hormone is produced by the fertilized egg and later the placenta, it’s a useful hormone to detect pregnancy.

What is the hCG Test and How Is It Done?

Women who are suspected of pregnancy can tell if they are pregnant with an hCG test from blood or urine. These tests are easily done at home and also in health centers. It is detected earlier in blood than in urine.

The test made from the blood sample taken from the arm can clearly measure the amount of the hormone and determine the actual level of hCG while giving information about the approximate week of pregnancy. The hCG test in the urine can only give information as if there is a pregnancy or not. The most suitable sample for a urine test is the first urine in the morning.

Can the hCG Test Be Used in the Diagnosis of Other Diseases Apart from Pregnancy?

hCG levels have been used in the multiple markers testing for trisomy 21 (Down Syndrome) in both the first and second trimesters of pregnancy.
In some types of cancers hCG is secreted, such as ovarian cancer, and also hCG is used to determine whether men have testicular cancers.
hCG may also be elevated in cancers of the stomach, pancreas, large intestine, lung, or liver.
It is used in the follow-up of the diagnosis and treatment of hydatiform mole, which is called grape pregnancy in women.
If pregnancy is suspected before any medical intervention, an hCG test should be performed.

How are hCG Test Values Evaluated?

It may differ depending on the laboratory where the hCG test is performed, the method used, or the instruments in which hCG is measured. The hCG hormone is measured in milli-international units per milliliter (mIU/mL).

hCG values represent the following:

Negative: < 5 IU/L,
Indeterminate: 5-25 IU/L,
Positive: >25 IU/L.

When hCG value is below 50 U/L, it can be re-measured at 48-hour intervals to monitor whether the hCG has increased.

The average levels of hCG in a pregnant woman’s blood are:

3 weeks: 6 – 70 IU/L
4 weeks: 10 - 750 IU/L
5 weeks: 200 - 7,100 IU/L
6 weeks: 160 - 32,000 IU/L
7 weeks: 3,700 - 160,000 IU/L
8 weeks: 32,000 - 150,000 IU/L
9 weeks: 64,000 - 150,000 IU/L
10 weeks: 47,000 - 190,000 IU/L
12 weeks: 28,000 - 210,000 IU/L
14 weeks: 14,000 - 63,000 IU/L
15 weeks: 12,000 - 71,000 IU/L
16 weeks: 9,000 - 56,000 IU/L
16 - 29 weeks (second trimester): 1,400 - 53,000 IUL
29 - 41 weeks (third trimester): 940 - 60,000 IU/L

A transvaginal ultrasound should be able to show at least a gestational sac once the hCG levels have reached between 1,000 – 2,000 mIU/mL. Because levels can differentiate so much and conception dating can be wrong, a diagnosis should not be made by ultrasound findings until the hCG level has reached at least 2,000 mIU/mL.

Are early home pregnancy tests accurate?

At-home urine tests detect whether a pregnancy has occurred. hCG hormone begins to be secreted at a measurable rate about 7-10 days after fertilization occurs. However, if the home pregnancy test is done in the early period, the result may be negative so it is necessary to wait for the menstrual day for the test.

Various tests available on the market have different sensitivities. Some tests identify lower levels of the hormone, while others may require the secretion of higher levels of hCG to detect pregnancy. If the test result is negative but still the period has not come, a pregnancy test should be done again.

When a false positive pregnancy test result?

Some Medicines:

Anti-anxiety medications, like diazepam (Valium) or alprazolam (Xanax)
Some antipsychotics, such as clozapine or chlorpromazine
Anticonvulsants, like phenobarbital or other barbiturates
Parkinson’s disease medications, including bromocriptine (Parlodel)
Some diuretics, like furosemide (Lasix, Diuscreen)
Antihistamines, including promethazine
hCG injection in the treatment of infertility- trigger shot
Chemotherapy

A recent miscarriage or abortion.

Certain medical conditions:

Molar pregnancy,
Urinary tract infection,
Kidney disease that causes blood or white blood cells in the urine,
Germ cell tumors of the ovary, a type of ovarian cancer,
Pituitary problems (very rarely).

What do low hCG levels mean?

Chemical pregnancy: A chemical pregnancy occurs if a fertilized egg, known as the embryo, is unable to implant, or grow, very early on. This can happen for many reasons. Some causes of chemical pregnancies are unknown.
Blighted ovum
Miscarriage
Ectopic pregnancy
Miscalculation of last menstrual period.
The abnormally low values be associated with adverse pregnancy outcomes. In the absence of fetal chromosomal or structural anomalies, there is conflicting data regarding an association between abnormal hCG levels and pregnancy outcomes. Some studies have shown a significant association between low hCG levels and adverse pregnancy outcomes, including fetal loss, intrauterine growth restriction, and low birth weight while others have not demonstrated such associations.

What do high levels of hCG mean?

Multiple pregnancies (twins, triplets, or more)
Molar pregnancy
Miscalculation of last menstrual period.
The relationship between elevated hCG and adverse pregnancy outcomes is controversial. Several studies have shown that increased levels of second-trimester hCG were associated with a number of pregnancy complications including late fetal loss, gestational hypertension, pre-eclampsia, intrauterine growth restriction, preterm delivery, and dead fetus in utero whereas some other studies did not find such associations.

When can a pregnancy test be done in IVF treatments?

A pregnancy test can be done 14 days after egg retrieval, twelve days after day 3 embryo transfer, or 10 days after day 5 embryo transfer in IVF (in Vitro Fertilisation) treatments. The blood test or a urine test will detect and measure hCG, the “pregnancy hormone.” The hCG level generally doubles every 2-3 days in early pregnancy.

An early at-home pregnancy test during IVF treatment does give false results.

Summary

HCG values are not a simple blood test, they include many clinical conditions about whether the pregnancy is healthy, as well as other diseases other than pregnancy. the hCG test results should be evaluated together with the doctor's examination. Although there are possible findings of pregnancy and hCG values show pregnancy, the definitive diagnosis of a healthy pregnancy is made by seeing the gestational sac and the baby’s heartbeat on ultrasound examination.