Babies of women who continued smoking after becoming pregnant were born an average 100 grams lighter than those born to women who did not smoke, according to findings in a landmark survey.
The results of the survey, the first large-scale nationwide study of its kind in Japan, prompted one researcher to warn that babies born with a low birth weight were at future risk of obesity and heart disease.
Smoking during pregnancy is said to lower the amount of oxygen and nutrients that reach the fetus as well as stunt its growth.
The survey found that of the 9,369 babies studied by the University of Yamanashi, those of smokers were estimated to weigh less at birth by an average of more than 100 grams compared with those born to women who do not smoke.
The babies in the study were born in 2011, with adjustments to the data made for factors such as the weight of mothers and their financial situation.
"If the birth weight is low, there is a bigger risk (of a child) suffering from obesity and heart disease in the future," said Zentaro Yamagata, a University of Yamanashi professor involved in the study.
"If you find out that you are pregnant, the sooner you quit smoking, the smaller the impact will be on the child," Yamagata said.
The survey found that boys born to women who have never smoked weighed on average about 3,096 grams, while those born to smokers weighed about 2,959 grams. When would-be mothers stopped smoking during the early stages of their pregnancy, their baby boys weighed around 3,068 grams.
According to the survey, girls born to nonsmokers weighed on average about 3,018 grams, babies of smokers weighed some 2,893 grams.
Meanwhile, the birth weight for babies of women who stopped smoking in the early stages of pregnancy was on average 2,978 grams.