On a global scale, the most common causes of stillbirth are complications during childbirth, infections like syphilis during pregnancy, health problems like high blood pressure or diabetes, fetal growth restriction - in which babies fail to grow at the proper rate - and birth defects.

Most miscarriages, on the other hand, happen in the first trimester and most are believed to be due to random genetic abnormalities.

Still, certain lifestyle habits have been tied to a higher risk of miscarriage, including heavy drinking, drug use and, in some studies, smoking.

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 households.

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,” he concluded. “We need to enact laws to protect these babies.”

SOURCE:  BJOG: An International Journal of Obstetrics and Gynecology, online March 23, 2011.