Smoking, as well as second-hand smoke, is very harmful to the developing baby. Nicotine and carbon monoxide are the most harmful components. They both result in decreased oxygen to the baby.
The risk of fetal death and preterm delivery is doubled in mothers who smoke. Smoking (and second-hand smoke) also increase the risk of Sudden Infant Death Syndrome (SIDS) and learning disorders.
If you are a smoker, or if you live with a smoker, this is a very good time for you or your partner to stop. Talk to your health care provider about ways to quit smoking.