The hCG hormone, short for human chorionic gonadotropin, is produced by human embryos and young fetuses prior to the formation of the placenta. The purpose of hCG is to communicate to a woman's body that she's pregnant, inducing changes in her reproductive cycle and hormone levels that help maintain the pregnancy.
Reproduction
Each month, your body prepares for conception. This process begins when an egg matures in one of your ovaries. As the egg ripens, tissue around the egg starts secreting progesterone and estrogen, hormones that cause the uterine lining to thicken. Once you ovulate, the tissue that surrounded the egg remains in the ovary--it's now called the corpus luteum--and continues to secrete estrogen and progesterone. After around 14 days, the corpus luteum disintegrates, and the lining of the uterus sloughs.
Fertilization
If the egg that you ovulate meets with a sperm and you conceive, it's the responsibility of the dividing egg to communicate to your body that you're pregnant so that you don't slough the uterine lining. The dividing cell ball, called a zygote, will need to embed in the uterine lining and receive nutrients and oxygen in order to survive. As such, the zygote secretes hCG, which maintains your corpus luteum. This, in turn, maintains the uterine lining.
HCG and Pregnancy
The primary role and benefit of hCG, simply stated, is to maintain the uterine lining until such time as the corpus luteum is no longer necessary. Around the third or fourth month of pregnancy, the developing baby--now called a fetus--has completed its formation of an organ called the placenta, which takes over the role of providing oxygen and nutrients. The placenta also secretes progesterone, which maintains the uterine lining and renders the corpus luteum obsolete, Dr. Lauralee Sherwood explains in her book "Human Physiology."
HCG Levels
Your hCG levels, if you're pregnant, should double approximately every 48-72 hours during early pregnancy. They will reach their peak around the 12th week of gestation, Heidi Murkoff and Sharon Mazel explain in their book "What To Expect When You're Expecting." If your hCG levels don't reach the concentrations they should, this can indicate--or lead to--a problem with the pregnancy, up to and including loss of the pregnancy due to sloughing of the uterine lining.
Other Benefits
A secondary benefit of hCG is that it may help to prevent exposure of developing babies to environmental toxins. High concentrations of hCG during early pregnancy lead to morning sickness, which in turn causes women to become quite sensitive to food and substances in the environment. An article published by Drs. Samuel Flaxman and Paul Sherman in the June 2000 "The Quarterly Review of Biology" suggests that those women who have more morning sickness--a phenomenon related to higher hCG levels--are less likely to give birth to babies with toxin-related birth defects.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "What to Expect When You're Expecting"; Heidi Murkoff and Sharon Mazel; 2008
- "The Quarterly Review of Biology"; Morning Sickness: A Mechanism For Protecting Mother and Embryo; Samuel Flaxman and Paul Sherman; June 2000
