The toxins in cigarette smoke cross the placenta and collect in the fetus

If a woman smokes while she's pregnant, or lives with a smoker during her pregnancy, her baby has a head start on so-called "second-hand smoke." That concerns Dr. Shabih Hasan, a pediatrician from the University of Calgary in Canada.

He wanted to study smoke exposure in infants, but says he couldn't study the exposure in humans. So he looked at the experience of rat pups to see what would happen if their mothers smoked while they were pregnant.

Hasan experimented with two groups of pregnant rats. One group was exposed to cigarette smoke by breathing the smoke through their noses, as humans would.

"And it was right throughout the pregnancy, for 10 to 12 puffs per cigarette, and 10 cigarettes a day and 10 [milliliters] of volume," Hasan says. "So we calculated, it leads to the plasma level, or the level in blood, of smoking material the same as it will be in humans."

The other group was not exposed to smoke at all.

After the rat pups were born, Hasan exposed them to several stressors. First, he put them into a hot environment. Then he increased the stress by reducing the amount of oxygen in their air.

"When we lowered their oxygen and increased their temperature, [the smoke-exposed rat pups] started to gasp twice as much as the control [group]," Hasan reports. "And when you remove the low oxygen stress, they continued to gasp for quite some time and it was a very long time before they recovered."

Hasan says these reactions are thought to be similar to what happens to human babies born to mothers who smoke. And these children are at higher risk of dying from SIDS – Sudden Infant Death Syndrome. Hasan says what he found in the smoke-exposed rats might compare the experience of some SIDS victims.

Scientists don't know for sure what causes respiratory problems in the children of smokers. Hasan says some have pointed to the thousands of chemicals present in cigarette smoke, including carbon monoxide and hydrogen cyanide – both toxins.

"This is transmitted to the fetus, and all the carcinogens of cigarette smoke cross over to … the fetus very, very quickly and remain there in a much higher amount than on the other side," Hasan explains. "One speculation is that when you give carbon monoxide and hydrogen cyanide through smoke, it changes the brain's receptors and it probably changes probably the baby's ability to sense oxygen so that they cannot sense it, or some other changes happen."

Hasan says as these children grow, they remain at risk of many smoking-related diseases, and anything that can be done to help parents quit is a benefit to the entire family.

Hasan's research is published in the American Journal of Respiratory and Critical Care Medicine.