Chemicals in the body called hormones, play vital roles in causing a pregnancy to occur, supporting the developing fetus during the pregnancy as well as helping the birth to occur and breast milk to be formed. As explained by the University of Maryland Medical Center a hormone called human chorionic gonadotropin or hCG is one of the first chemical signs of a pregnancy and is the marker for clinical and home pregnancy tests. HCG and other important hormones including estrogen and progesterone steadily increase as the early pregnancy progresses. These hormones prove critical for conception and for initiating and supporting the changes and growth needed for a successful pregnancy and birth.
Human Chorionic Gonadotropin (hCG)
Human Chorionic Gonadotropin or hCG is a hormone produced by the cells of the fertilized egg and the placenta and increases until about day 70 of the pregnancy, as explained by the American Pregnancy Organization. It is produced even before the zygote or fertilized egg implants, which makes it a good marker for determining if a woman has become pregnant. Levels of hCG can double every 72 hours during early pregnancy. It promotes the production of another important pregnancy hormone, progesterone and causes a variety of symptoms of early pregnancy including nausea, vomiting and severe fatigue.
Progesterone
Progesterone maintains the lining of the uterus so that the fertilized egg can implant and pregnancy can occur, says the Expectant Mother's Guide website. Very small amounts of progesterone first become produced by the corpus luteum--the cyst that forms after ovulation, when the egg leaves the ovary. If the egg does not become fertilized, then progesterone levels dip and the lining of the uterus sheds causing menstruation. However, if the egg becomes fertilized it begins secreting hCG which signals the corpus luteum to keep secreting progesterone until the placenta forms and begins producing large amounts of progesterone several weeks later. Progesterone levels increases 10 times higher than normal during pregnancy because this hormone proves necessary to promote the growth of blood vessels in the walls of the uterus and to prevent the uterus from contracting and causing a miscarriage or premature birth. Progesterone also causes side effects such as severe fatigue during pregnancy, says the Merck Online Medical Library website.
Estrogen
The hormone estrogen proves responsible for ovulation--the release of the egg from the ovary into the fallopian tube. Several types of estrogen hormone exist and two of these estradiol and androgen cause changes in the vagina, cervix and uterus to increase the chances of fertilization. Later, the placenta produces large amounts of estrogen causing levels to rise during pregnancy. This hormone proves important for increasing blood flow to the uterus to help support the pregnancy. At late stages of pregnancy, estrogen promotes the production of another hormone called prolactin, which causes lactation--milk production--in the mother, says the University of Maryland Medical Center.
