We all think we know the story of pregnancy. Sperm meets egg, followed by nine months of nurturing, nesting, and quiet incubation. But this story isn’t the nursery rhyme we think it is. In a way, it’s a struggle, almost like a tiny war. And right on the front lines of that battle is another major player on the stage of pregnancy that not a single person on the planet would be here without. An entirely new organ: the placenta.