Human chorionic gonadotropin (hCG) is a hormone produced by the syncytiotrophoblast, a component of the fertilized egg, after conception. Following implantation, the syncytiotrophoblast gives rise to the placenta.
Blood or urine tests measure hCG. These can be pregnancy tests. hCG-positive indicates an implanted blastocyst and mammalian embryogenesis. These can be done to diagnose and monitor germ cell tumors and gestational trophoblastic diseases. As pregnancy tests, quantitative blood tests and the most sensitive urine tests usually detect hCG between 6 and 12 days after ovulation. However, it must be taken into account that total hCG levels may vary in a very wide range within the first 4 weeks of gestation, leading to false results during this period of time. Gestational trophoblastic disease like hydatidiform moles ("molar pregnancy") or choriocarcinoma may produce high levels of ßhCG (due to the presence of syncytialtrophoblasts- part of the villi that make up the placenta) despite the absence of an embryo. This, as well as several other conditions, can lead to elevated hCG readings in the absence of pregnancy. HCG levels are also a component of the triple test, a screening test for certain fetal chromosomal abnormalities/birth defects. Most tests employ a monoclonal antibody, which is specific to the ß-subunit of hCG (ß-hCG). This procedure is employed to
ensure that tests do not make false positives by confusing hCG with LH and FSH. (The latter two are always present at varying levels in the body, whereas the presence of hCG almost always indicates pregnancy.) Many hCG immunoassays are based on the sandwich principle, which uses antibodies to hCG labeled with an enzyme or a conventional or luminescent dye. Pregnancy urine dipstick tests are based on the lateral flow technique.The urine test may be a chromatographic immunoassay or any of several other test formats, home-, physician's office-, or laboratory-based. Published detection thresholds range from 20 to 100 mIU/ml, depending on the brand of test. Early in pregnancy, more accurate results may be obtained by using the first urine of the morning (when hCG levels are highest). When the urine is dilute (specific gravity less than 1.015), the hCG concentration may not be representative of the blood concentration, and the test may be falsely negative.The serum test, using 2-4 mL of venous blood, is typically a chemiluminescent or fluorimetric immunoassay that can detect ßhCG levels as low as 5 mIU/ml and allows quantification of the ßhCG concentration. The ability to quantitate the ßhCG level is useful in the monitoring germ cell and trophoblastic tumors, follow-up care after miscarriage, and in diagnosis of and follow-up care after treatment of ectopic pregnancy. The lack of a visible fetus on vaginal ultrasound after the ßhCG levels have reached 1500 mIU/ml is strongly indicative of an ectopic pregnancy. Concentrations are commonly reported in thousandth international units per milliliter (mIU/ml). The international unit of hCG was originally established in 1938 and has been redefined in 1964 and in 1980. At the present time, 1 international unit is equal to approximately 2.35×10-12 moles, or about 6×10-8 grams.
*hCG levels in weeks from LMP (gestational age)*
3 weeks LMP: 5 – 50 mIU/ml
4 weeks LMP: 5 – 426 mIU/ml
5 weeks LMP: 18 – 7,340 mIU/ml
6 weeks LMP: 1,080 – 56,500 mIU/ml
7 – 8 weeks LMP: 7, 650 – 229,000 mIU/ml
9 – 12 weeks LMP: 25,700 – 288,000 mIU/ml
13 – 16 weeks LMP: 13,300 – 254,000 mIU/ml
17 – 24 weeks LMP: 4,060 – 165,400 mIU/ml
25 – 40 weeks LMP: 3,640 – 117,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml
Postmenopausal females: <9.5 mIU/ml
-These numbers are just a GUIDELINE because every woman’s level of hCG can rise differently. It is not necessarily the level that matters but rather the change in the level.
*Now is IMPORTANT TO KNOW*
The hormone human chorionic gonadotropin (better known as hCG) is produced during pregnancy. It is made by cells that form the placenta, which nourishes the egg after it has been fertilized and becomes attached to the uterine wall. Levels can first be detected by a blood test about 11 days after conception and about 12 - 14 days after conception by a urine test. In general the hCG levels will double every 72 hours. The level will reach its peak in the first 8 – 11 weeks of pregnancy and then will decline and level off for the remainder of the pregnancy.
-In a bout 85% of normal pregnancies, the hCG level will double every 48 – 72 hours. As you get further along in pregnancy and the hCG level gets higher, the time it takes to double can increase to about every 96 hours.
-Caution must be used in making too much of hCG numbers. A normal pregnancy may have low hCG levels and result in a perfectly healthy baby. The results from an ultrasound after 5 - 6 weeks gestation are much more accurate than using hCG numbers.
-An hCG level of less than 5mIU/ml is considered negative for pregnancy, and anything above 25mIU/ml is considered positive for pregnancy.
-The hCG hormone is measured in milli-international units per milliliter (mIU/ml).
-A transvaginal ultrasound should be able to show at least a gestational sac once the hCG levels have reached between 1,000 – 2,000mIU/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.
-A single hCG reading is not enough information for most diagnoses. When there is a question regarding the health of the pregnancy, multiple testings of hCG done a couple of days apart give a more accurate assessment of the situation.
-The hCG levels should not be used to date a pregnancy since these numbers can vary so widely.
-There are two common types of hCG tests. A qualitative hCG test detects if hCG is present in the blood. A quantitative hCG test (or beta hCG) measures the amount of hCG actually present in the blood.
-What can a high hCG level mean?
A high level of hCG can also mean a number of things and should be rechecked within 48-72 hours to evaluate changes in the level. A high hCG level can indicate:
Miscalculation of pregnancy dating
-Should my hCG level be checked routinely?
It is not common for doctors to routinely check your hCG levels unless you are showing signs of a possible problem. A health care provider may recheck your levels if you are bleeding, experiencing severe cramping, or have a history of miscarriage.
-What can I expect of my hCG levels after a pregnancy loss?
Most women can expect their levels to return to a non-pregnant range about 4 – 6 weeks after a pregnancy loss has occurred. This can differentiate by how the loss occurred (spontaneous miscarriage, D & C procedure, abortion, natural delivery) and how high the levels were at the time of the loss. Health care providers usually will continue to test hCG levels after a pregnancy loss to ensure they return back to <5.0
-Can anything interfere with my hCG levels?
Nothing should interfere with an hCG level except medications that contain hCG. These medications are often used in fertility treatments, and your health care provider should advise you on how they may affect a test. All other medications such as antibiotics, pain relievers, contraception or other hormone medications should not have any effect on a test that measures hCG.