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 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 e-mail. “Some of these trans-placental substances may affect foetal programming of the kidney during pregnancy.”
Shinzawa and colleagues examined data from 44,595 children. The outcome of interest was the presence of proteinuria at age 3 defined as urinary protein >/= 1+.
Data on maternal smoking was collected during women’s prenatal check-ups, and researchers also had records from their children’s health check-ups at four, nine, 18 and 36 months of age.
Overall, 79 per cent of women said they never smoked and another four per cent said they stopped smoking during pregnancy. About 17 per cent of the mothers said they continued to smoke while pregnant.
One more nail in the coffin
The absolute risk of proteinuria among the children was low. But proteinuria was 24 per cent more likely in children born to mothers who smoked while pregnant.
The frequencies of child proteinuria was 1.7 per cent in children born to smokers, 1.6 per cent in those whose mothers were former smokers and 1.3 per cent in children born to women who never smoked.
Children exposed to second-hand smoke at home also appeared to have a higher risk of proteinuria 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 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 hypertension and renal injury in adults,” Fowler, who wasn’t involved in the study, added by e-mail.
“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.”