If you cannot stop smoking completely, at least try to reduce the amount of cigarettes you are smoking. Take small steps. If you have success with reduction, a few weeks or months later, you might be able to reduce the amount even further. Therefore, there will be a lot less harm throughout the pregnancy to the baby. The baby is still at risk for the harmful effects of smoking even after delivery.
Smoking can decrease the amount of milk production.
Nicotine may be passed in the breast milk for about two hours after the mother has smoked. It also important to note that even if a woman is not breastfeeding, the baby still can be exposed to the harmful effects of secondhand smoke. This link contains a fact sheet with information about smoking and pregnancy. The American Lung Association also provides information on quitting smoking. The March of Dimes provides research and resources on delivering healthy babies.