Nicotine pumped by smoking mothers into their babies growing inside the wombs is known to affect the brain's development, causing long-term behavioral and learning impairment. A 2007 research found that nicotine in the breast milk shortens a baby's sleep time.

And this new Japanese research points to another blow to the overall health: Mothers smoking in the first three moths of pregnancy will deliver children that are about thrice more likely to experience obesity later during their development. Still, the new research did not find a precise cause for this, one theory being that children of mothers who smoke experienced nutrition shortage while in the uterus. Also, by skipping the breakfast during pregnancy, mothers increased by 2.4 times the likelihood of their children developing obesity.

The team led by Zentaro Yamagata, professor at Yamanashi University's School of Medicine, made the two decades long survey on 1,400 Japanese women who became mothers between April 1991 and March 1997. The researchers managed to gather data on about 1,000 of these children till they entered fourth grade at age 9 or 10, and the results were announced recently at a meeting of public health experts in Japan, being scheduled to be published by December.

The obesity likelihood was increased by 2.9 times in the case of the children whose mothers smoked when they were three months pregnant or before, compared with children of non-smoking mothers.

The data "indicate smoking during pregnancy, even in the early stages, can affect the health of children over a long period of time. Researchers can "speculate" that children who had been poorly fed in the womb would stock up on nutrition after they were born. But we don't know the truth. What is important here is to stop smoking," said Yamagata.

"There have been studies around the world about the linkage between smoking during pregnancy and child obesity, but continuous research on the same group of children until they turn 10 is very rare", he added.