How Smoking Harms Babies in the Womb

Consider the physiological effects of smoking on yourself and your baby, especially the increased risk of SIDS.

1. It retards growth. Smoking stunts the growth of the developing fetus. Nicotine narrows the uterine blood vessels, thus reducing blood flow to the baby. Also, smoking puts the oxygen blocker carbon monoxide into the blood that nourishes baby. Carbon monoxide robs oxygen from the baby. Levels of carbon monoxide have been measured at six to seven times higher in the blood of pregnant mothers who smoke. Carbon monoxide levels in cigarette smoke resembles that of automobile exhaust. Smoking thus reduces the oxygen supply to the infant in the womb, in effect slightly smothering the defenseless baby.

2. It retards brain development. Nicotine has been shown experimentally to retard fetal brain growth in animals. The developing brain is particularly vulnerable to low levels of oxygen, and immaturity of the brain center that regulates breathing could contribute to SIDS. Recent studies of smoking mothers' infants who died in the womb provide insight into how exposure to smoking may injure developing brains. Besides causing neurological damage by lessening oxygen supply to the developing brain, nicotine may be poisonous to area of the brain directly involved with heart and breathing functions and arousal from sleep. Also, infants whose mothers smoked during pregnancy are more likely to have diminished arousal from sleep in response to a low-oxygen challenge.

3. It impairs breathing after birth. Mothers who smoked at least half a pack of cigarettes a day during pregnancy are nearly three times more likely to have babies with mucus-blocked airways or episodes of apnea.

4. It increases the likelihood of prematurity. The risk of SIDS goes up as baby's birthweight and gestational age go down. Babies of smoking mothers end up being smaller (due to intrauterine growth retardation), and smoking increases the risk of complications of pregnancy that lead to prematurity: premature rupture of fetal membranes, placenta previa, and premature detachment of the placenta.

5. Passive smoking also harms the baby. When expectant mothers are exposed to smoke from other people's cigarettes, their babies are also exposed. One study showed that a pregnant woman's exposure to smoke for at least two hours a day doubled her risk of delivering a low birthweight baby. While older studies claimed no increased SIDS risk if the father smoked, a newer study reports a higher risk of SIDS if the father smokes. Demand that your husband and co-workers respect the life inside your womb. If your job requires working in a smoke-contaminated environment while pregnant, know that this is a proven health hazard to your baby and is grounds for reassignment to a baby-healthy environment. As a testimony to the wisdom of the body, many mothers find they have an aversion to being around cigarette and cigar smoke (and to drinking alcohol) while pregnant. Listen to the warnings of your body and hundreds of medical studies: Don't expose yourself and your baby to smoke while pregnant. Legally, you have the right to work in a smoke-free environment.

6. Other ways smoking harms babies and pregnant mothers include:

• Increases infertility (smoking could account for ten percent of infertility problems in mothers)
• Increases risk of ectopic pregnancy
• Increases risk of placenta previa
• Increases risk of premature separation of the placenta
• Increases risk of placental abnormalities (known as "smoker's placenta")
• Increases risk of problem pregnancies, e.g., pre-eclampsia
• Increases risk of prematurity under intrauterine growth retardation
• Increases risk of the newborn dying at birth by twenty percent; thirty-five percent if mother smokes more than thirty-five cigarettes a day
• Increases risk of respiratory infections in infant
• Increases risk of SIDS by two to five times

Studies have shown the following correlations between mothers who smoke during pregnancy, especially heavy smoking (greater than one pack a day) and the development of their children. Children of mothers who smoked during pregnancy are more likely to show:

• Decreased newborn Apgar scores (if smoking more than one pack a day)
• Decreased mental performance scoring at age one year
• Decreased academic performance scores in the school-age child
• Reduced I.Q.
• Shorter stature (by one to two centimeters)
• Smaller head circumference as infants
• Increased learning difficulties (children were 25 percent more likely to have learning disabilities if their mother smoked greater than 20 cigarettes a day)
• Increased hyperactivity
• Increased behavioral problems

Studies on the long-term effects of smoking during pregnancy on children's mental and physical development did not all agree. Some showed slight or no adverse effects. The above conclusions represent the general consensus of outcome studies.