Estrogen refers to a group of hormones present in the female body: estradiol, estriol and estrone. During the course of your life, the levels of these estrogen hormones fluctuate. They help to regulate your menstrual cycle and are also key in supporting and maintaining a healthy pregnancy. After childbirth, estrogen levels plummet, remaining artificially low until you stop breastfeeding.
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What Estrogen Does
Ovaries produce estrogen. A woman in her childbearing years has between 20 and 750 picograms per milliliter (pg/mL) of estradiol -- the main type of estrogen -- in her blood. During pregnancy, the placenta also produces a small amount of estrogen. Estrogen helps your uterus grow during pregnancy, increases the size and capacity of your blood vessels and prepares your mammary glands for lactation. According to the website Real Age, a woman produces more estrogen in one day of pregnancy than in three years of her non-pregnant life. Because estrogen is crucial for sustaining pregnancy, estrogen production in the ovaries ramps up in your menstrual cycle after you ovulate, dropping after your period begins.
Estrogen After Childbirth
During pregnancy, estrogen production soars. However, in the 24 hours immediately following delivery your estrogen levels plummet to pre-pregnancy levels. This rapid decrease in hormone levels may be one of the causes of postpartum depression. Depending on the woman, it takes several months for ovulation to happen again after childbirth; this means the level of estrogen remains low until a monthly cycle resumes.
Estrogen and Breastfeeding
Breastfeeding may suppress your body's monthly menstrual cycle. This is because high levels of prolactin -- a hormone that helps support breastfeeding -- competes with the production of other hormones, like estrogen and progesterone, that are crucial for a normal menstrual cycle. In fact, estrogen -- including artificial sources from estrogen-only birth control pills -- inhibits milk production. Symptoms of low estrogen during breastfeeding are similar to symptoms of low estrogen during menopause; they include vaginal dryness, night sweats and hot flashes, fatigue, depression and insomnia.
Estrogen After Breastfeeding
The cyclical production of estrogen -- rising levels after the egg is released, following by falling levels during the menstrual phase -- does not return in some women until after they have completely weaned their baby from breastfeeding. In other women, especially those who wean slowly, estrogen production gradually returns to pre-pregnancy levels, even while still nursing. The return of normal estrogen levels means you are once again having a normal monthly cycle -- and monthly periods -- and are fertile.