Why do you think pregnant women/women who just gave birth "glow'?

My theory is: "DUH!!" I'm so tired of people saying "Oh shes just glowing after the birth of blahblahblah." No fake. Shes been drinking tons of water and taking all of her vitamins and not smoking and exercising and not drinking and eating really well for 9 months... that will do good for anyones skin... Its not the alien she had growing inside her for 9 months that mad her glow... its that she was taking care of herself. Pregnant or not, doing the aforementioned things will give you good skin and make you radiant. Agree or disagree??? Thanks for you opinions!