Smoking, pregnancy and the fetus.

Smoking may influence a women's reproductive ability by having adverse effects on fertility, the early embryo and the fetus. The ability to become pregnant and to maintain the pregnancy long enough for it to be clinically detected is reduced in smokers. Smoking can adversely influence several of the crucial steps within the reproductive process required for achieving a pregnancy. Despite the increased miscarriage rate in women that smoke there is no evidence to suggest that smoking can cause fetal abnormalities. The chemical composition of cigarette smoke is more closely related to reduction in fetal growth than the number of cigarettes smoked. In smokers, the placenta appears remarkably normal. The effects of smoking could be due to one or more of the hundreds of different chemical substances in tobacco smoke, but apart from carbon monoxide and nicotine, little is known about the effects of other toxins. Nicotine can adversely affect uterine and placental blood flow by causing constriction of the blood vessels. It can also affect both the maternal and fetal blood pressure and heart rate, but its action on the fetal cardiovascular system does not appear to be dependent on its effect on placental perfusion.