I'm a nurse and work in Pulmonary (lung specialists). Cigarette smoke can cause low birth weight. Cigarette smoking ESP one or two a day will not effect your baby's lungs. Cigarette smoking does not effect development except by low birth weight. We've also noticed babies born to women who smoke are more colicky than babies born to women who don't smoke. You should quit smoking because its bad for you and we see new cancer pt's everyday. Also when your baby is born don't smoke in your home since 2nd hand smoke is worse than smoking yourself.
Smoking is not good for your baby, even one or two. It causes problems with development and can cause problems with your baby lungs leading to asthama and other things. when someone has smoked throughout the pregnancy a Dr. will tell them its ok to have 1 or 2 because at that point they think it would be worse to put the baby through withdrawls from the nicotine.