Pregnancy causes a great many changes in a woman’s body as it prepares to grow and nourish a baby. Hormones cause most of these changes, with estrogen being one of the most important. Estrogen contributes not only to maintaining the pregnancy via progesterone, but also to other vital areas of fetal development and regulation.
One of estrogen's main roles in fetal development is to maintain pregnancy. To do this, estrogen, which is produced by the placenta during pregnancy, regulates progesterone production. Progesterone plays many crucial roles during pregnancy, including keeping the uterus from contracting, maintaining a safe environment in the uterus for the baby, promoting breast growth and fighting off dangerous cells that might injure the fetus. Since progesterone is so critical to the well-being of the fetus, keeping proper estrogen levels is important. In fact, studies have shown that dropping estrogen levels during a pregnancy often correlates with miscarriage.
Estrogen is responsible for proper growth of fetal internal organs like the lungs and kidneys, as well as the reproductive organs. Also, estrogen promotes placental growth, which is crucial for proper development of the baby. It maintains both uterine blood flow and the endometrium, assists with lactation and regulatates fetal bone density. Finally, estrogen protects females in the womb from the effects of male hormones.