Human chorionic gonadotropin, or hCG, is the pregnancy hormone. Your doctor may order one of two types of hCG tests. A qualitative hCG test determines if hCG is present in the blood and can confirm pregnancy. A quantitative hCG test, or beta hCG, records the level of hCG in the blood. High levels of hCG may be benign, but they also may indicate a serious medical condition, so additional testing is necessary.
Definition
HCG is a byproduct of the cells that form the placenta. Increased hCG levels first appear approximately 11 days after conception. In 85 percent of pregnancies, levels of this hormone double every two to three days until hCG reaches its peak, somewhere in the 8-to-11-week range, according to the American Pregnancy Association. After this point, hCG levels decline, then remain relatively steady for the rest of the pregnancy.
Limitations
Because hCG levels vary widely among pregnant women, a single hCG reading does not provide sufficient information for a diagnosis, according to the American Pregnancy Association. To get a better sense of possible health concerns, doctors normally order multiple hCG tests two or more days apart. Your doctor also may order other testing, such as an ultrasound or other blood tests, to get a more complete picture of your fetus' status. Some medications that contain hCG---primarily drugs used for infertility treatments--can provoke inaccurate hCG readings.
Molar Pregnancy
A molar pregnancy, or a hydatidiform mole, is one possible cause of elevated hCG levels, according to the Mayo Clinic. This happens when there is a genetic error during fertilization that leads to abnormal, but noncancerous, cell growths within the uterus. In most cases, there is no embryo, but rather a mass of cysts that grow very rapidly. In some cases, however, there is an abnormal embryo that begins to grow, but it is malformed and cannot survive. Molar pregnancy can pose serious health risks to the mother, including the possibility of a rare form of cancer. Extended follow-up care is essential and will increase the chances of a viable pregnancy in the future.
Down Syndrome
High hCG levels also are associated with Down syndrome, a genetic abnormality caused by an extra copy of chromosome 21, according to DrGreene.com. One method for detecting Down syndrome is a triple blood screening for high hCG, low alpha fetoprotein and low unconjugated estriol. This blood test detects almost 90 percent of Down syndrome cases before birth, but it has a high false positive rate. Doctors usually order an ultrasound in the 10th through 14th week of pregnancy to confirm the results of the blood tests.
Other Causes
Since hCG levels increase rapidly in the early phases of pregnancy, a high hCG level may indicate that you and your doctor have miscalculated the date of conception and you are more advanced in your pregnancy than you believed. Another possibility is that you are pregnant with more than one child. The placenta produces hCG, so in the case of multiple fetuses, the additional placenta or placentas will produce more hCG.
