If all pregnant women stopped smoking we could reduce the rate of stillbirths by 11 percent and newborn deaths by 5 percent.
Cigarette smoke contains more than 2,500 chemicals, and both nicotine and carbon monoxide are thought to be related to adverse outcomes in pregnancy. Smoking nicotine has been associated with several complications of pregnancy.

It appears to double a woman’s risk of developing placental problems, including placenta previa (a low-lying placenta that covers part or all of the opening of the uterus), placental abruption (the placenta peels partially or completely away from the uterine wall prior to delivery), and premature rupture of the membranes.
Cigarette smoking is known to cause lower birth weight and size; mothers who smoke 13 or more high-tar cigarettes a day have smaller babies in poorer condition than those of nonsmoking mothers.

Smokers have a miscarriage rate twice as high as that of nonsmokers, and babies born to mothers who smoke have more than double the risk of dying of sudden infant death syndrome.
Women who smoke may experience more ectopic pregnancies (a potentially dangerous situation in which the fertilized egg attaches to, and grows on, the fallopian tube outside the uterus).
Children of smokers may have far more respiratory illnesses (like asthma) than those of nonsmokers.

Even secondhand smoke is seriously harmful to mother and baby and should be avoided when possible.
The more a woman smokes, the greater the risk to her baby. However, if she stops smoking before the end of her first trimester, she is no more likely to have a lower birth weight baby than a nonsmoking woman.

Even stop smoking by the third trimester of pregnancy can improve the baby’s growth.