SMOKING AND REPRODUCTION

In all of its dimensions, the reproductive process is impaired by the use of tobacco, particularly cigarette smoking.  Problems can be found in association with infertility, problem pregnancy, breastfeeding, and the health of the newborn.  So broadly based are reproductive problems and smoking that the term fetal tobacco syndrome or fetal smoking syndrome is regularly used in clinical medicine.  Some physicians even define a fetus being carried by a smoker as a “smoker” and, upon birth, as a “former smoker.”

Infertility

Recent research indicates that cigarette smoking by both men and women can reduce levels of fertility.  Among men, smoking adversely affects blood flow to erectile tissue, reduces sperm motility, and alters sperm shape, and it causes an overall decrease in the number of viable sperm.  Among women, the effects of smoking are seen in terms of abnormal ovum formation, including a lessened ability on the part of the egg to prevent polyspermia, or the fertilization by multiple sperm.  Smoking also negatively influences estrogen levels, resulting in underdevelopment of the uterine wall and ineffective implantation of the fertilized ovum.  Lower levels of estrogen may also influence the rate of transit of the fertilized egg through the fallopian tube, making it arrive in the uterus too early for successful implantation or, in some cases, restricting movement to the point that an ectopic, or tubal, pregnancy may develop.  Also, the early onset of menopause is associated with smoking.

Problem pregnancy

The harmful effects of tobacco smoke on the course of pregnancy are principally the result of the carbon monoxide and nicotine to which the mother and her fetus are exposed.  Carbon monoxide from the incomplete oxidation of tobacco is carried in the maternal blood to the placenta, where it diffuses across the placental barrier and enters the fetal circulation.  Once in the fetal blood, the carbon monoxide bonds with the fetal hemoglobin to form fetal carboxyhemoglobin.  As a result of this exposure to carbon monoxide, the fetus is progressively deprived of normal oxygen transport and eventually becomes compromised by chronic hypoxia.

Nicotine also exerts its influence on the developing fetus.  Thermographs of the placenta and fetus show signs of marked vasoconstriction within a few seconds after inhalation by the mother.  This constriction further reduces the oxygen supply, resulting in hypoxia.  In addition, nicotine stimulates the mother’s stress response, placing the mother and fetus under the potentially harmful influence of elevated epinephrine and corticoid levels.  Any fetus exposed to all of these agents is more likely to be miscarried, stillborn, or born prematurely.  Even when carried to term, children born to mothers who smoked during pregnancy have lower birth weights and may show other signs of a stressful intrauterine life.

Breastfeeding

For women who decide to breastfeed their infants, smoking during this period will continue to expose their children to the harmful effects of tobacco smoke.  It is well recognized that nicotine appears in breast milk and thus is capable of exerting its vasoconstricting and stress-response influences on nursing infants.  Mothers who stop smoking during pregnancy should be encouraged to continue to refrain from smoking while they are breastfeeding.

Neonatal Health Problems

Babies born to women who smoked during pregnancy will, on average, be shorter and have a lower birth weight than children born to nonsmoking mothers.  During the earliest months of life, babies born to mothers who smoke experience an elevated rate of death caused by sudden infant death syndrome.  Statistics also show that infants are more likely to develop chronic respiratory problems, be hospitalized, and have poorer overall health during their early years of life.  Problems such as those just mentioned may also be seen in children of nonsmoking mothers, when they were exposed prenatally to environmental tobacco smoke.  In addition, environmental tobacco smoke exposure extending beyond the home and into the workplace may increase the probability of problem pregnancies and neonatal health problems.  Most recently, the interest in the effects of tobacco smoke on pregnancy has been extended to include behavioral differences seen in infants born to women who smoked during pregnancy.

Parenting, in the sense of assuming responsibility for the well-being of children, does not begin at birth, but during the prenatal period.  In the case of smoking, this is especially true.  Pregnant women who continue smoking are disregarding the well-being of the children they are carrying.  Other family members, friends, and coworkers who subject pregnant women to cigarette, pipe, or cigar smoke are, in a sense, exhibiting their own disregard for the health of the next generation.