It is well documented that smoking during pregnancy can increase the chances of a wide variety of pregnancy complications. In fact, tobacco is one of the leading causes of prenatal problems.
Among the more serious of these problems are vaginal bleeding, miscarriage, abnormal placental implantation, premature placental detachment, prematurely ruptured membranes, and early delivery. It has been suggested that as many as 14 percent of preterm deliveries are related to cigarette smoking.
There is also strong evidence that an expectant mother's smoking adversely affects her baby's development in the uterus. The most widespread risk is low birth-weight. In industrialized nations, smoking is blamed for as many as a third of all babies who are born too small - and being born too small is the major cause of infant illness and perinatal death (those that occur just before, during, or after birth).
Babies of smoking mothers are more likely to suffer from apnea (breathing lapses) and are twice as likely to die of SIDS (sudden infant death syndrome, or crib death) as babies of nonsmokers. In general, babies of smokers are not as healthy at birth as babies of nonsmokers.
There is also evidence that, on average, babies of smokers may never catch up to the children of nonsmokers, that they may have long-term physical and intellectual deficits, and that they may also be hyperactive. At age 14, one study showed, children of smokers tended to be more prone to respiratory disease, to be shorter than children of nonsmokers, and to be less successful at school.
It was once believed that the reason for the deficiencies these children display was poor prenatal nutrition in that the mothers smoked rather than ate during their pregnancies. But recent studies disprove this theory. Smoking mothers who eat as much and gain as much weight as nonsmoking mothers still give birth to smaller babies. This seems to be the result of carbon monoxide poisoning and a reduction of oxygen to the fetus through the placenta.