Smoking and Pregnancy
Leaving a Legacy

Teenage daughters are four times more likely to smoke if their mothers smoked while pregnant, a risk that remained even when researchers controlled for social influences, according to a study conducted at Columbia University. Researchers theorized that nicotine, which can cross the placental barrier, stimulates a fetus' receptors for dopamine, the brain chemical involved with drug addiction. This "priming" may predispose girls to smoke. Animal studies have shown prenatal nicotine does affect certain brain activity once the animal is grown. Prenatally exposed boys weren't at risk, possibly because male hormones may protect them. -AP wire service report, 1994

Maternal Smoking Linked to Mental Retardation

A study looked at whether maternal smoking contributed to serious intellectual deficits such as mental retardation. Given that smoking appeared in previous studies to have even a slight effect on IQ scores, it may be that the prevalence of mental retardation--defined as an IQ score less than 70--could be increased by maternal smoking in children not known to have central nervous system damage.

In a study conducted between 1987 and 1989, 221 ten year olds with idiopathic mental retardation (not attributable to any know central nervous system damage), served as the case population and 400 children attending normal public schools served as the control group. Most of the mentally retarded children had IQs between 50 and 70. An interview was conducted with the mother of each child to inquire about reproductive history and her use of cigarettes and alcohol during pregnancy. Information about pregnancy and delivery was obtained from medical records.

Women were considered smokers if they smoked at least five cigarettes a week during pregnancy. Twenty-four percent of the control group mothers and 35 percent of the mothers of mentally retarded children smoked during pregnancy. The smokers were 75 percent more likely to have children with mental retardation than the non-smokers, an increased risk that was reduced but not eliminated when potentially confounding factors such as birthweight were taken into account.

Eleven percent of mothers in the control group and 15 percent in the case group smoked more than one pack of cigarettes per day during pregnancy, with many of these women continuing to smoke heavily into the second trimester. Heavy smokers were more likely to have children with mental retardation than non-smokers.

Smoking during pregnancy was therefore found to increase the risk of a child being mentally retarded at age ten by 50 percent, with a higher risk among heavy smokers. If this in fact represented a causal relationship between smoking and mental retardation, it would mean that one in three cases of idiopathic mental retardation among children of women who smoked during pregnancy could be attributed to smoking. However, a causal relationship has not been established. It is not yet known how fetal exposure to cigarette smoke would work to increase the risk of mental retardation. It could have a direct toxic effect or alter nutrition during pregnancy, or reduce the amount of oxygen available to the fetus. Further possibilities are that exposure to smoke after birth affects behavior or development, or that smoking mothers respond to their children differently. -Dr. Carolyn Drews et al, "The relationship between idiopathic mental retardation and maternal smoking during pregnancy,"

Why Smoking Affects Weight Gain

Recent evidence indicates that the poor weight gain associated with smoking during pregnancy may not be caused by reduced food consumption as was previously thought, but by an increased need for calories. It has been suggested that inhaled carbon monoxide lowers the efficiency of energy metabolism and that nicotine increases the metabolic rate. Each of these effects could lead to a lower weight gain in pregnant smokers. Because carbon monoxide and nicotine cross the placenta and appear in the fetal blood in higher concentrations than in maternal blood, it is likely that these components of cigarette smoke contribute to poor fetal weight gain in the same way that they affect maternal weight gain.

Plasma levels of beta carotene among smokers have been reported to be substantially below those of nonsmokers despite similar dietary intkes, and smokers have been reported to need up to twice as much ascorbic acid as nonsmokers to maintain a similar body pool. -Nutrition During Pregnancy and the Postpartum Period: A Manual for Health Care Professionals, California Department of Health Services, 1990

Eliminating Toxins

As smoking is eliminated, stored toxins in tissues and cells will begin to pour into the body. Drinking plenty of water will help the body eliminate them quickly. Eating two large and varied servings of fresh vegetables daily will help women replace lost nutrients and add roughage so the bowels can detoxify at their peak efficiency. Whole grains and legumes will help replace depleted B vitamins. Zinc helps maintain healthy mucus membranes. -Anne Frye, Holistic Midwifery Volume I, Care During Pregnancy, Labrys Press, 1995

Antioxidant Vitamins

Antioxidant vitamins may help reduce the damage that smoking causes to the placenta. These findings may have important implications for preventing growth retardation in the fetuses of pregnant women who continue to smoke. A study of more than 1,500 pregnant women confirmed previous findings on the effects of smoking on placental tissue. Specifically, smoking promotes calcification of the placenta, which may cause intrauterine growth retardation and fetal distress in labor. But researchers at the University of Tennessee and other centers also found that higher intakes of the antioxidant vitamins E, C and beta-carotene could be linked to less calcification of placental tissue caused by smoking. In the study, the amount of daily antioxidants each woman consumed was calculated using the results of interviews with nutritionists. With greater dietary intake of vitamin E, the researchers found less placental calcification. A similar trend was noted for intakes of vitamin C and beta-carotene, but this finding was restricted to African-American women. The researchers suggest that a diet rich in antioxidants may also be important for pregnant nonsmokers whose placentas may be at increased risk of damage due to pregnancy-induced high blood pressure or exposure to environmental pollutants. -American Journal of Epidemiology 147, 1998 as reported in Midwifery Matters, Summer 1998

Reprinted from Midwifery Today E-News (Vol 1 Issue 11, Mar. 12, 1999)
To subscribe to the E-News write:
For all other matters contact Midwifery Today:
PO Box 2672-940, Eugene OR 97402
541-344-7438,, Midwifery Today Home
       ---> Resources
       ---> Risk Factors