Pregnant women that smoke cigarettes on a daily basis can greatly harm their fetus. The Tobacco smoke in cigarettes greatly reduces fetal growth through the presence of nicotine, carbon monoxide, hydrogen cyanide, cadmium and various other aromatic hydrocarbons, but the two most dangerous chemicals that are found in cigarettes are nicotine and carbon monoxide. Nicotine causes the babies heart rate to speed up, reduces placental vascularisation, constricts the placental arteries, and thickens the endothelium of placental blood vessels. This creates a reduction in the placental blood flow, and further reductions in oxygen delivery. As well nicotine interferes with the ability of the placenta to feed the baby the nutrients it requires. Therefore the babies growth is slowed down. Carbon monoxide causes growing cells to be starved of oxygen, and effects the brain. This can lead to a low birth weight and higher chance of the baby dying at birth. Smoking is the single largest modifiable( changeable) risk factor in fetal growth retardation. Maternal smoking during pregnancy is also associated with genetic defects as well as an increased incidence of congenital malformations such as cleft palates, microcephalus, and clubfoot. Mothers who smoke one pack a day during pregnancy have an 85% increased risk of having a child with mental retardation. Mothers that smoke during their pregnancy have double the chance of having a child with behavural problems.

             Another one of the biggest factors that disrupts fetal growth and development is alcohol. This is a very common substance abuse of pregnant women. Everytime the pregnant mother is drinking, her fetus is also drinking. The alcohol crosses the placental barrier, and goes directly into the fetus"s liver. The ethanol found in alcohol may impair the nutrient support of the fetus. Acetaldehyde, a major metabolite, crosses the placenta and is teratogenic. Since the alcohol stays in the fetus for a long time, the small liver is unable to metabolize the alcohol.