Maternal, fetal, and placental blood flow change when pregnant women smoke, although the long-term health effects of these changes are not known. Some studies suggest that smoking during pregnancy causes birth defects such as cleft lip or palate.

Smoking mothers produce less milk, and their babies have a lower birth weight. Maternal smoking also is associated with neonatal death from Sudden Infant Death Syndrome (SIDS), the major cause of death in infants between one month and one year of age.