Is it ok to smoke occasionally during pregnancy?

No. The problem is that people who say they smoke occasionally either underestimate how much they are truly smoking or can suddenly develop a more regular habit of smoking. Each cigarette introduces 1000s of toxins into the baby's system and raises the mother's blood pressure possibly causing an early separation of the placenta.
No. Ideally, no smoking during the pregnancy is preferred. If one is currently a smoker, have realistic goals to slowly wean down to zero upon discovering that you are pregnant. Ask your obgyn to help with a plan to reach this goal with low chance of rebounding. There are many local support groups, as well as web-based tools online to accomplish this difficult, yet healthy goal.
No. Is it ok if I have just a little poison? According to the centers for disease control & prevention- research shows that smoking during pregnancy is linked to premature births, babies with low birth weights & stillbirths, as well as sudden infant death syndrome. The mother’s health can also be compromised. See: http://www.Cdc.Gov/tobacco/basic_information/health_effects/pregnancy/.