NEW YORK (Reuters Life!) - Pregnant women who live or work with smokers may be at slightly higher risk of having a stillborn baby, giving birth to a slightly smaller baby or having a baby with a smaller head, according to a Canadian study.
Secondhand smoke is thought to expose people to about one percent of the smoke that active smokers inhale, and the study adds to evidence that even passive smoking can harm unborn babies.
"This information is important for women, their families and healthcare providers," wrote Joan Crane, of Eastern Health in St. John's, Canada, in the BJOB: An International Journal of Obstetrics and Gynaecology.
"Undiluted sidestream smoke contains many harmful chemicals and in greater concentration than cigarette smoke inhaled through a filter."
Crane and colleagues noted that those chemicals may harm the fetus in a variety of ways -- for instance, by restricting blood flow and possibly damaging the placenta.
Using a database of pregnant women from the Canadian provinces of Newfoundland and Labrador, they looked at the rate of stillbirths as well as other birth outcomes, such as head circumference, which has been linked to the later intellectual development of children.
Of nearly 12,000 women in the database, 11 percent said they had been exposed to secondhand smoke.
The rate of stillbirth, in which the baby dies during the third trimester of pregnancy, was 0.83 percent in passive smokers and 0.37 percent in women who didn't breathe tobacco fumes.
This doesn't prove that smoke itself was the culprit, yet when researchers accounted for other risk factors -- including age and the women's drinking and drug habits -- passive smokers still had three times the odds of stillbirths.
In other words, if smoke is indeed to blame, one extra baby would die in the womb for every 117 women exposed.
"This is huge," said Hamisu Salihu, an expert on stillbirth at the University of South Florida in Tampa.
"We can now inform patients to secondhand smoke means they can lose their baby."
That link had not been firmly established until now, Salihu, who was not involved in the study, told Reuters Health.
The Canadian researchers also found that babies born to passive smokers weighed 54 grams, or nearly 2 ounces, less than babies whose mothers lived and worked in smoke-free places.
And their heads were slightly smaller too, measuring 0.24 centimeters (about 0.1 inch) less on average.
Salihu said head circumference has been associated with IQ, although the link is indirect.
"Policy makers should really take this matter seriously. We need to enact laws to protect these babies," Salihu added.
On a global scale, the most common causes of stillbirth are complications during childbirth, infections during pregnancy such as syphilis, health problems such as high blood pressure or diabetes, fetal growth restriction -- in which babies fail to grow at the proper rate -- and birth defects.