HCG stands for human chorionic gonadotropin- it's a hormone that you don't normally produce, but if you're pregnant you have it in your bloodstream. HCG comes from tissue in a developing embryo, and it helps to inform your body that you're pregnant, which allows you to maintain the pregnancy. Your obstetrician may check your hCG at several points during pregnancy.
HCG Production
The purpose of hCG, explains Dr. Lauralee Sherwood in her book "Human Physiology," is to keep a group of hormone-producing cells in the ovary from disintegrating. This group of cells, called the corpus luteum, forms each month around the time of ovulation and helps your uterine lining thicken. In the absence of hCG, the group of cells disintegrates and you menstruate. If you conceive a child, the embryo secretes hCG, which maintains the corpus luteum.
Uterine Lining
Your early pregnancy success depends upon the integrity of the uterine lining. Until such time as your developing baby has finished forming the placenta--around the third or fourth month of pregnancy--it's completely dependent upon the uterine lining for oxygen and nourishment, explains Dr. Gary Thibodeau in his book "Anatomy and Physiology." As such, an appropriately high hCG level helps ensure that your pregnancy survives its early weeks.
HCG Count
The developing embryo starts producing hCG very soon after fertilization. Conception takes place at the end of week two of pregnancy, and by the end of week three of pregnancy, most women have measurable concentrations of hCG in the blood. According to AmericanPregnancy.org, hCG levels can vary greatly even within a normal pregnancy--by the end of the third week, your hCG count can be anything from 5 to 50 mIU/mL.
Pregnancy Test and HCG Count
You can use your hCG to determine whether or not you're pregnant. Home pregnancy tests check for hCG in the urine--if you have it in the blood, the kidneys will filter it into the urine. Most women have enough hCG in the urine for a pregnancy test to come up positive by the middle or end of the fourth week of pregnancy.
Your Obstetrician and Your HCG
Your obstetrician may also test your hCG one or more times during your early pregnancy. This is because during normal pregnancies, hCG counts double every 48 to 72 hours, explains AmericanPregnancy.org. If your hCG levels double appropriately, that is an indication that your pregnancy is progressing normally. hCG levels that don't double appropriately could indicate a problem, such as an ectopic pregnancy. Your doctor can perform additional tests to determine the nature of the problem if you have a low hCG count.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
- American Pregnancy Association: hCG Count
