The levels of female hormones change drastically with age. Hormones are usually present at birth, increase during puberty and pregnancy, and then decrease as women approach menopause. The results of decreased hormone levels include both infertility and uncomfortable symptoms such as hot flashes and headaches. Thus, many aging women try to replace the fading hormones with manufactured substitutes for estrogen and progesterone, which can also be used in different forms to prevent pregnancy during the childbearing years.
Female hormones are present from birth, causing some babies — male or female — to have enlarged breasts during infancy. This may be a result of estrogen passing from the mother to the baby through the placenta, or it could be caused by the baby's own body making prolactin in response to the sudden drop of estrogen from its body once the umbilical cord is cut. Some baby girls experience occasional breast enlargement for the first couple years of life, showing that hormones affect their life early on.
During puberty, the hypothalamus produces the gonadotrophin-releasing hormone, which in turn signals to the pituitary gland to release additional hormones. These include the luteinizing hormone (LH) and the follicle-stimulating hormone (FSH), both of which stimulate the ovaries to make additional hormones. The most well-known female hormones produced by the ovaries are estrogen and progesterone, which assist LH and FSH in regulating the menstrual cycle. These hormones increase the levels of estrogen just before ovulation, and then increase the levels of progesterone for about two weeks afterward. When the released egg is not fertilized, the progesterone level drops, which makes the uterine lining begin to shed in what is called menstruation.
Pregnancy and female hormones go hand-in-hand, as the lack of the usual drop in progesterone does not occur when a woman gets pregnant, which is why her period never shows up during that cycle. Instead, human chorionic gonadotrophin (hCG) signals to the ovaries to make more progesterone and estrogen, though the placenta usually takes over this job just before the second trimester. The results of higher levels of these female hormones are increased blood supply, a thicker uterine lining, and uterine muscles that are relaxed enough to grow with the unborn baby. While prolactin increases to make breast milk just before the birth of the baby, both estrogen and progesterone levels drop suddenly after the birth, sometimes resulting in postpartum depression. These female hormones start to decrease even more as menopause approaches.
Falling levels of estrogen during menopause can result in issues for the bones and heart, such as osteoporosis and heart disease. Night sweats, hot flashes and vaginal dryness are also common symptoms of a loss of this sex hormone. Headaches and fatigue may occur, too, leading to discomfort during menopause. On the other hand, lower levels of progesterone lead to infertility, vaginal dryness and low libido. Weight gain, depression and bloating are all additional consequences of the reduced levels of progesterone that come with menopause.
For these reasons, hormone replacement therapy (HRT) is often used by aging women who dislike the effects of lower levels of female hormones. HRT usually comes as a pill or patch to be placed on the body, and it can reduce symptoms such as hot flashes and night sweats. Prior to menopause, some women use synthetic hormones to prevent pregnancy, because the excess estrogen in many types of birth control can prevent ovulation. The progesterone that comes in many forms of birth control can thicken cervical mucus to make it hard for sperm to get to the cervix, and it can also make the uterine lining too thin for an embryo to implant.