Smoking is very detrimental for pregnant women. Researchers showed in a study that mothers who smoke during pregnancy may increase the risk of having children with lower birth weights, and also they found that smoking doesn’t appear to have any affect on other areas of development.

A study of almost 53,000 children born in the US during the 1960s confirmed a long acknowledged link between smoking during pregnancy and a higher risk of low birth weight.

Researchers found also that children born to smoking mothers were more likely to be overweight by age 7 than those born to non-smoking mothers.

Researchers are unsure yet about the cause of the link, some said that nicotine may affect the developing brain in a way that influences appetite control later in life.

Scientists reported no findings of any direct link between smoking during pregnancy and various developmental problems.

In their first study researchers noted some associations between smoking during pregnancy and various developmental problems. However, those links disappeared after researchers factored in the family environment - such as parents' income and education, and whether the child lived with both parents.

They added that a child’s home environment has a greater impact on physical and cognitive development than being born to mothers who smoke.

"Smoking still causes cancer, smoking still causes heart disease, and we still find a strong effect of smoking on birth weight, and we know that low birth weight can have negative consequences," said Dr. Stephen Gilman, of the Harvard School of Public Health in Boston.

Gilman and his colleagues based their findings on data from a study that included more than 2,000 sets of siblings whose mothers had smoked during one pregnancy but not the other. Gilman are sure that if maternal smoking, itself, can affects children's IQ, school performance and other aspects of development, then differences should be apparent among these siblings too.