Your Estrogen Level Soars
What happens: That spiffy new organ of yours, the placenta, churns out estrogen faster than a multiplex pops popcorn. In fact, you produce more estrogen in 1 day when you're pregnant than you do in 3 years when you're not pregnant. And you'll make more in one pregnancy than you will during the rest of your nonpregnant life. Production peaks right before birth.
Why it happens: Extra estrogen is critical to you and your developing baby. It stimulates the growth of the uterus, enlarges your milk ducts, and makes the cells that line your vessels secrete nitric oxide, which opens them up. This ensures that blood can run freely to and from your placenta, bringing in nutrients, ferrying out waste, and creating the perfect little darling who will soon be trying to eat Tupperware.