Pregnant teens in Australia are deliberately taking up smoking to help them reduce the birth weight of their unborn babies and make childbirths less dangerous and painful, a shocking new research has found.

According to a 10-year study into smoking in Australia, girls as young as 16 are taking up smoking as they are more afraid of labour pains linked to having a large child rather than the health complications caused by cigarettes.

"They had read on packets that smoking can reduce the birth weight of your baby, which is obviously not how the public health message is intended to be taken," said Simone Dennis, associate professor at the Australian National University.

"They were scared because they were small. The worst thing that could happen to them was to have an enormous baby," Dennis was quoted as saying by 'The New Zealand Herald'.

"Some had even taken it up for the first time for that very reason, and some smoked harder, hoping the promise on the packet would come true," she said.

The findings are published in the book Smokefree.