HCG, or human chorionic gonadotropin, is also called the pregnancy hormone. HCG is manufactured by the cells that form the placenta, which is the organ that develops in a woman's uterus to provide nourishment to the fetus throughout pregnancy. More HCG is released in a pregnancy with multiple fetuses than in a single pregnancy. The presence of HCG in a woman's urine indicates pregnancy, and home pregnancy tests measure for HCG to determine if the result will be displayed as positive or negative.
When HCG is Released
When a sperm fertilizes an egg, it begins an approximately nine-day trip down through the fallopian tubes and into the uterus. Implantation occurs when the fertilized egg attaches itself to the uterine wall and HCG begins production shortly thereafter. Initial HCG levels are so low that they will not be detectable in urine until several days later. HCG levels are measured in milli-international units per milliliter (mIU/ml).
When HCG is Detectable
Home pregnancy tests, available at most drug stores and other retailer stores, vary in their HCG sensitivity levels. Some tests are able to detect HCG in urine before a missed menstrual period, while others cannot detect the hormone until one week past the missed period. In general, any measurement below 5 mIU/ml is considered negative for pregnancy and any measurement above 25 mIU/ml is considered positive. In the vast majority of normal pregnancies, HCG levels double every 48 to 72 hours.
HCG Levels in Pregnancy
HCG levels continue to increase and then begin to slowly decrease throughout the course of the pregnancy. Levels also vary from woman to woman. Basic guidelines indicate that a pregnant woman who is just three weeks past her last menstrual period, or LMP, will measure 5 to 50 mIU/ml; a woman nine to 12 weeks past her LMP will measure 25,700-288,000 mIU/ml; and a woman 25 to 40 weeks past her LMP will measure 3,640-117,000 mIU/ml.
Low or High HCG Levels
HCG levels that are abnormally low or high may indicate issues with the pregnancy or the presence of multiples. Since exact HCG levels are not shown on a home pregnancy test, women who are concerned about their specific HCG levels should consult their physician for testing. Low levels may indicate the miscalculation of conception date, an impending miscarriage, blighted ovum or ectopic pregnancy. High levels may indicate miscalculation, a molar pregnancy or the presence of multiples fetuses.
Blood Tests for HCG
HCG is also present in the blood of a pregnant woman. Your physician may conduct a blood test to see if HCG is present and to measure the exact amount of HCG. Blood testing for HCG may also be used as a screening for birth defects, which are usually conducted between 15 and 20 weeks gestation. The levels of HCG, along with the level of other substances and the woman's age, help to determine if the baby may have certain birth defects.
