What about alcohol, caffeine and tobacco?

There is no known safe amount of alcohol a woman can drink while pregnant, according to the Centers for Disease Control (CDC). However, some doctors say an occasional glass of wine may be okay. To be on the safe side, don't drink at all. But if you do drink, know that "more is worse," Dr. Dominguez says. "I tell people that a glass or two glasses every once in a while is not a big deal. I think that over two glasses, you have to be careful," she says.

The CDC also recommends limiting caffeine during pregnancy. Dr. Dominguez tells her patients not to drink more than three cups of coffee per day. Remember, caffeine is also found in tea, chocolate and some sodas.

Tobacco use, meanwhile, isn't healthy for you or your baby. Smoking during pregnancy may raise the risk of low birth-weight babies, miscarriages, infant mortality and other problems. It's also a good idea to avoid secondhand smoke during pregnancy.