Women smokers trying for babies take longer to conceive than non-smokers, Oxford scientists have revealed.

Researchers have found that would-be mothers with a tobacco habit take an average of two months longer to become pregnant.

They also found that those who give up cigarettes a year before trying to conceive take no longer to become pregnant than women who have never smoked.

The study was led by Dr Marcus Munafo, of the Imperial Cancer Research Fund, based at the Institute of Health Sciences at the Churchill Hospital, Oxford.

He said: "The risks of smoking during pregnancy are well documented, including higher infant mortality, the increased risk of the baby developing serious respiratory infection and lower birth weights.

"But many women may not be aware that by quitting, they are also greatly improving their chances of getting pregnant."

Dr Munafo said many women changed their lifestyle while trying for a baby, by cutting their alcohol intake, taking vitamins and minerals and eating a healthy diet. He said smoking, which affected hormone function, ovulation and the quality of eggs, should also be given up as part of the pre-pregnancy routine.

More than 550 women were questioned for the research, published in Wednesday'sJournal of Biosocial Science.

Dr Munafo said: "The message from this research is that if you want to get pregnant, you will not only improve your chances by quitting, you will also be doing something to protect the health of your child in the long term."