It is estimated that maternal smoking causes 5,000 extra perinatal deaths each year in the United States.

Environmental tobacco smoke exposure and maternal smoking during pregnancy have been shown to cause lower infant birth weights.

A recent study has proposed that maternal smoking during pregnancy can lead to future teenage obesity.

"This is greater than the effect of maternal smoking during pregnancy," write the researchers.

In other studies information on maternal smoking during pregnancy was not available.

As an obesogen, nicotine mostly acts on prenatal development after maternal smoking occurs.

A strong association has been made between maternal smoking and childhood overweight/obesity, with nicotine as the single causal agent.

Current research suggests that several genes are likely to control risk, as well as environmental factors such as maternal smoking.

Other environmental factors, such as maternal smoking, estrogenic compounds in the diet' and endocrine-disrupting chemicals may be important also.

But research announced on Sunday suggests a way in which maternal smoking might also contribute to childhood cancers, as some have suspected.