Risks of Smoking During Pregnancy

by Pregnancy.org Staff

pregnant and smoking"Don't eat lunch meat!" "Exercise regularly." "Limit fish intake."... Advice for protecting your unborn baby leaps at you from all directions. No smoking is high on the list. Does stopping smoking really make a difference for you and your baby?

Definitely! Women who quit smoking before or early in pregnancy significantly reduce the risk for several adverse outcomes.

Risks to Mom

Compared with women who do not smoke:

  • Women who smoke prior to pregnancy are about twice as likely to experience a delay in conception and have approximately 30% higher odds of being infertile.
  • Women who smoke during pregnancy are about twice as likely to experience premature rupture of membranes, placental abruption, and placenta previa during pregnancy.

Risks to Baby

Babies born to women who smoke during pregnancy:

  • Have about 30% higher odds of being born prematurely.
  • Are more likely to be born with low birth weight (less than 2500 grams or 5.5 pounds), increasing their risk for illness or death.
  • Have a higher incident of certain birth defects
  • Weigh an average of 200 grams less than infants born to women who do not smoke.
  • Are 1.4 to 3.0 times more likely to die of Sudden Infant Death Syndrome (SIDS).

Cigarette smoke contains more than 2,500 chemicals, with nicotine, tar, and carbon monoxide thought to be the most dangerous to the fetus. Recent research has linked maternal smoking and exporuse to second hand smoke with the following issues and concerns:

Sudden Infant Death Syndrome

Smoking during pregnancy is a two-edged sword. It raises likelihood of a preterm baby and increases the likelihood the baby will have impaired respiratory function.

Babies born prematurely to women who smoked during their pregnancy may be at higher risk of sudden infant death syndrome (SIDS) than premature infants born to nonsmoking moms, new research from the University of Calgary suggests.

The Canadian study compares the breathing reflexes of "preemies" born to smokers versus nonsmokers. The researchers found that these tiny babies were more likely to have impaired recovery from pauses in breathing if their mother had smoked during her pregnancy.

"Our study shows that preterm infants make incomplete and/or delayed recovery from interruptions in breathing," study author and neonatologist Dr. Shabih Hasan, a professor of pediatrics at the University of Calgary, said in an American Thoracic Society news release. "This has clear implications for their risk of SIDS."

Oral-Facial Birth Defects

Smoking during the first trimester is associated with an increase in two common oral-facial birth defects, cleft lip and cleft palate. Study measured levels of a cotinine, a metabolite of nicotine, to determine if the mothers had smoked during pregnancy. Women who smoked were nearly 2.5 times more likely to have babies with oral clefts.

Behavior Changes and Withdrawal Symptoms

Babies whose mothers smoked 6-7 cigarettes or more a day were more jittery, more excitable, stiffer, and more difficult to console. The symptoms were similar to those found in newborns of women who use crack cocaine or heroin while pregnant. The data suggest “neonatal withdrawal” from nicotine, said the authors.

Even at 10 weeks of age, after the affects of nicotine would be quite reduced, babies exposed to maternal smoking were more irritable and difficult to sooth.

Reduced Blood Flow to the Fetus

-- Babies whose moms smoked during pregnancy have smaller head sizes, measure shorter, and weigh less. Prenatal exposure to cigarette smoke retards fetal growth. Why?

"This study in one of the first to show a biochemical measurement of what is going on to cause the lower birth weight," said study author Malene Rohr Andersen, project manager of the Department of Clinical Biochemistry at Gentofte University Hospital. Analysis showed a 47% drop in levels of a protein, endothelial nitric oxide synthase (eNOS), that helps blood vessels to relax and blood flow to increase. These babies also experienced an 18% reduction in plasma levels of "good" HDL.

"We have known for 50 years that infants born to mothers who smoke during pregnancy have lower birth weights. But this study provides a possible explanation of why there is restricted blood flow to the fetus. Reduced production of the vasodilator nitric oxide may lower the blood flow to the fetus."

Higher Systolic Blood Pressure

Babies born to women who smoked had systolic blood pressure that was 5.4 points higher on average than that of babies born to nonsmokers researchers, at the University Medical Center, Utrecht found. Also significant was the finding that babies of smoking women in the study had significantly lower birth weights, were shorter and had a smaller chest circumference than babies of nonsmokers.
"Maternal smoking in pregnancy leads to adverse developmental changes," the authors conclude.

Congenital Heart Defects

A recent study suggests that women who smoke anytime during the month before pregnancy to the end of the first trimester are more likely to have a baby with birth defects, particularly congenital heart defects. The risk of heart defects appears to increase with the number of cigarettes a woman smokes.

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