If you're a non-smoker, but your partner lights up, your baby is still subjected to serious risks. In fact, the CDC says that women exposed to secondhand smoke have a 20 percent greater chance of delivering underweight babies than women who aren't exposed. Even women who spend a great deal of time around wood fires may experience similar negative effects due to inhalation of carbon monoxide. This risk, however, is smaller than the risk of smoking, and not something to be worried about if it occurs in moderation.