It appears that this is due to decreased oxygen to the fetus. Another effect is the likelihood of spontaneous abortion. In fact, this risk is almost double for women who smoke. There is also a clear relation between smoking and infant death syndrome. Babies born to cigarette smokers may be slower to develop, more likely to have brain function disorders, psychological abnormalities and lower intelligence scores.
Cigarette smoking is also a significant risk factor for hyperkinesis in children.
While smoking does not ensure damage to the child, it is an avoidable risk factor and the responsibility of the mother is great indeed.