Human chorionic gonadotropin, or hCG, is a hormone produced by the placenta early in pregnancy. Home pregnancy tests read levels of hCG to give a positive or negative pregnancy test result. Because these tests don't determine the exact amount of hCG in the urine, they're called qualitative tests, meaning they only determine that hCG is present or not present. Quantitative hCG tests specify the exact amount of hCG in the blood. Levels rise during the first two months of pregnancy and then level off; the normal range is quite variable.
Early Levels
A negative hCG level is usually reported by a laboratory as less than 5 milli-international units per milliliter, or mIU/ml. At the time of the first missed period, which is considered week four of pregnancy, hCG levels range from 5 to 426 mIU/ml, according to the American Pregnancy Association. A quantitative hCG of 43 mIU/ml is the norm at four weeks, the University of Iowa Laboratory Services reports. Lab values vary from lab to lab and women who ovulated later or earlier than normal in a given month may have higher or lower hCG levels. The most sensitive home pregnancy tests can detect hCG levels of 20 mIU/ml, Fertility Plus reports.
Normal Rises
Most medical practitioners consider the rise of the hCG levels to be more important than the actual numbers. In the first eight weeks of pregnancy, hCG levels double every 48 to 72 hours in around 85 percent of normal pregnancies, the APA reports. After eight to 11 weeks, the rise in hCG levels slows and then remains level as the placenta begins to produce progesterone. The purpose of hCG is to signal the corpus luteum, the leftover shell of the ovarian follicle that produced an egg, to keep making progesterone when pregnancy occurs.
Dropping Levels
If hCG levels fall or do not rise appropriately in early pregnancy, the pregnancy may not be viable. An ectopic pregnancy, one that implants outside the uterus, can also cause slow-rising hCG levels. Miscarriage may be inevitable in this case; since most miscarriages are caused by abnormal embryos, bed rest or medications will not prevent miscarriage. By week five or six of pregnancy, ultrasound results are usually more predictive of pregnancy viability than hCG levels. By the time hCG levels reach 2,000 mIU/ml, a gestational sac should be present on ultrasound.
Very High Levels
Very high hCG levels can indicate multiple pregnancy or may indicate abnormal placental growth, or a molar pregnancy. Some types of cancer also cause a rise in hCG levels in people who are not pregnant. An ultrasound can differentiate between a normal pregnancy and other causes of high hCG levels.
