Smoking during pregnancy is associated with a number of adverse maternal and fetal outcomes. It has been associated with placenta previa, abruptio placenta, premature rupture of membranes, preterm delivery, intrauterine growth restriction, Sudden Infant Death Syndrome (SIDS), and increased perinatal mortality rates. Because so many women smoke (26 percent of women of reproductive age in the United States and 20 percent of pregnant women), smoking represents a major public health problem.

Little is known about the nature of the dose-response relationship between tobacco exposure and these outcomes. Relationships are assumed to be linear, but this assumption has often been based on studies in which tobacco exposure has been defined categorically.