"Vitamin D works with calcium to help baby's bones and teeth develop. It's also essential for healthy skin and eyesight," says Trolice. All women, including those who are pregnant, need 600 international units of vitamin D a day, he says. Good sources include milk that's fortified with vitamin D and fatty fish, such as salmon. "Sunlight exposure also converts a chemical in the skin to vitamin D," he says, so make sure to spend a little time in the sun — with sunscreen, of course.