Tropin. Human chorionic gonadotropin. Sound Familiar? You may or may not have heard of hCG, but if you have, it may be because you read it on the box of your home pregnancy test. That's because hCG is the basis of home pregnancy tests. It's also the basis for the blood and urine pregnancy tests that your doctor performs. But there is much more to hCG than simply being an indicator of pregnancy.

HCG is a hormone produced by the placenta during pregnancy. It begins being produced and released into the blood almost immediately after the egg attaches to the uterine wall. Since hCG is released into the blood so soon after conception, it can be detected there even before your first missed menstrual period, as early as six days after implantation. Its function is to prevent the disintegration of the corpus luteum of the ovary and thereby maintain production of one of the main pregnancy hormones, progesterone.

HCG Levels HCG levels rise steadily for the first 14 to 16 weeks after your last menstrual period, doubling every 48- 72 hours in about 85% of normal pregnancies. After this time, the levels will slowly decrease. The increases in the hCG levels in early pregnancy can provide invaluable information about your pregnancy and the health of your baby. HCG levels return to zero shortly after pregnancy.

HCG levels are often measured as part of a maternal serum triple or quadruple screening test. These tests are done by measuring three or four substances in a woman's blood and are used to estimate the baby's risk of certain problems or congenital birth defects. The triple screen measures beta human chorionic gonadotropin (beta-hCG), alpha-fetoprotein (AFP), and a type of estrogen (unconjugated estriol or uE3). The quad screen measures the hormone inhibin-A in addition to the other three.

Abnormal hCG levels do not necessarily mean that there is a problem. It could simply be due to a miscalculation of pregnancy dating. Unfortunately though, abnormal hCG levels could also indicate a more serious issue. There are several things that could cause a high or low hCG level, so you should be retested within a few days to see how the levels are changing.

A high hCG level could be an indicator of a multiple pregnancy, in which there is more than one fetus present, or a molar pregnancy. A low hCG level could be an indicator of a possible miscarriage or blighted ovum, or an ectopic pregnancy, where the fertilized egg implants itself somewhere other than the uterus.

By now it should be apparent that you will be hearing quite a bit about hCG during your pregnancy, and now you will know more about what you are hearing.