A new study suggests that genes play a major role in how much cigarette smoking affects a baby's birth weight.
Cigarette smoking has long been linked to low-birth weight in newborns.
Despite evidence that mothers who smoke are putting their infants at risk, one in eight American women continue to smoke throughout their pregnancies.
That is according to Boston University School of Medicine researcher Xiaoban Wang. "Each year in the United States," she said, "300,000 babies are born with low-birth weight, meaning weighing less than 2.6 kilograms. And low-birth weight is a major determinant of infant death and also infant morbidity, meaning infant illness."
Dr. Wang adds that about 65 percent of all infant deaths occur among low-birth weight babies.
Dr. Wang and colleagues wanted to see what was going on at the genetic level that produced low-birth weight babies. In the Journal of the American Medical Association, they describe two genes that counteract the harmful chemicals of cigarettes. One of the genes is protective, the other is destructive.
The researchers studied over 700 women. Women who had the destructive gene but lacked the protective one had infants with the lowest birth weight. Their newborns weighed an average of 1.3 kilograms. The infants were also approximately three weeks premature.
Dr. Wang says there could be many other genes involved in birth weight. "In terms of whether we should screen for those kinds of genes, she said, "my answer [at] this stage is 'no'. The reason is low birth weight is a very complex entity caused by many environmental risk factors and genetic factors."
But one thing Boston University's Xiaoban Wang is certain of cigarette smoking is harmful and pregnant women should quit.