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Another reason not to smoke while pregnant

Kids whose mothers smoked while pregnant were 24 percent more likely to show signs of kidney damage in their urine tests by age three.

Women who smoke during pregnancy may be more likely to have children with kidney damage than mothers who steer clear of cigarettes, a study suggests.

Smoking during pregnancy has long been linked to preterm and underweight babies and a wide range of birth defects. The current study offers fresh evidence that the kidneys are among the organs at risk for damage, said lead author Dr. Maki Shinzawa, a public health researcher at Kyoto University in Japan.

“Cigarette smoking releases nicotine and other harmful or potentially harmful substances, such as nitrogen oxide, polycarbonate, and carbon monoxide, some of which cross the placenta,” Shinzawa said by email. “Some of these trans-placental substances may affect fetal programming of the kidney during pregnancy.”

Shinzawa and colleagues examined data from urine tests from 44,595 children to look for elevated levels of protein in the urine, which can indicate impaired kidney function.

Data on maternal smoking was collected during women’s prenatal checkups, and researchers also had records from their children’s health checkups at four, nine, 18 and 36 months of age.

Overall, 79 percent of women said they never smoked and another 4 percent said they stopped smoking during pregnancy. About 17 percent of the mothers said they continued to smoke while they were pregnant.

The absolute risk of kidney damage among the children was low. But compared with children born to nonsmoking mothers, kids whose mothers smoked while pregnant were 24 percent more likely to show signs of kidney damage in their urine tests by age three.

Urine tests showed elevated protein levels in 1.7 percent of children born to smokers, 1.6 percent of kids whose mothers were former smokers and 1.3 percent of children born to women who never smoked. Children exposed to second-hand smoke at home also appeared to have a higher risk of kidney damage than kids who didn’t live with smokers, but the difference wasn’t big enough to rule out the possibility that it was due to chance.

One limitation of the study is its reliance on women to accurately report and recall how much they smoked before or during pregnancy, and a lack of lab tests to confirm smoke exposure, the authors note in the Clinical Journal of the American Society of Nephrology.

Still, the findings add to evidence linking smoking to kidney damage, a connection that some previous research has established for adult smokers and for children who inhale second-hand smoke, said Dr. Paul Fowler, director of the Institute of Medical Sciences at the University of Aberdeen in the UK.

“Maternal smoking has been observed to lead to reduced kidney size in offspring, which is of concern since it is known that retarded kidney development contributes to (high blood pressure) and renal injury in adults,” Fowler, who wasn’t involved in the study, added by email.

“This study highlights one more reason why women should not smoke during pregnancy and why children should be raised in cigarette-free households,” Fowler said. “It is not, in itself, an overwhelming reason, but rather one more nail in the coffin.”

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