Now estrogen has many important functions during pregnancy, so its first important function is to actually generate the endometrium. But during pregnancy it serves three functions. It basically acts to actually enlarge our breasts of the woman, to basically prepare the woman for the process of lactation that takes place following birth. It also enlarges our uterus. And that's because as our fetus grows, the uterus must enlarge with our fetus. So it enlarges the uterus to accommodate the growing fetus.