NEW YORK (Reuters) -- Smoking during pregnancy is known to increase the risk of having a low birth weight child, possibly due to nicotine's ability to constrict blood vessels. Now, a new study suggests that infants of smokers enter the world with impaired lung function as well.
According to a report in this week's issue of The Lancet, researchers measured the lung function of more than 400 sleeping babies within 26 to 159 hours of birth. A decrease in time to the peak expiratory flow -- the amount of breathe exhaled -- was found in infants of mothers who smoked more than 10 cigarettes a day during pregnancy, mothers with high blood pressure in pregnancy and those with a family history of asthma.
The infants of smokers also weighed less (6.4 versus 6.8 pounds) and were shorter than (19 versus 19.4 inches) other babies. In the study, 238 women reported smoking during pregnancy, according to lead author Dr. S.M. Stick of the Department of Respiratory Medicine in Princess Margaret Hospital for Children in Perth, Australia.
However, the findings may be even stronger because blood tests revealed that 179 of the women classified as nonsmokers did indeed have some exposure to cigarette smoke. About 20 of the infants of "nonsmokers" had blood levels of cotinine -- a breakdown produce of nicotine -- high enough to indicate their mother's were active smokers.
"We therefore believe that our findings of an association between maternal smoking and [respiratory flow] would be strengthened if we could classify accurately all the infants expose in utero to tobacco smoke," Stick reported.
Children of mother's who smoke have long been known to have lung problems, including wheezing during infancy, asthma in later childhood, and reduced lung function in 6 year olds. However, it has been difficult to prove if lung problems are the result of smoke exposure before or after birth.
In the new study a unique method of measuring newborn lung function was used, called plethysmography. The researcher recorded breathing function with coils placed around the chest and abdomen, rather than using a face mask, which may interfere with accurate readings in very young infants.
"This approach reduces the risk that breathing patterns will be altered and is also less alarming for parents of newborns," Stick wrote.
It's not clear if reduced lung function in newborns causes lifelong breathing problems, but expiratory flow in older infants and young children and adult has been linked to airway obstruction.
"We speculate that [factors before birth] that reduce [expiratory flow] influence airway development, or the relative development of air spaces and airways resulting in small airways in relation to lung volume," Stick concluded.
SOURCE: The Lancet (1996;348:1060-1063)
