In Britain, 1050 pregnant women are being recruited for the most extensive trial of its kind to establish the effect of using nicotine patches during pregnancy.

The clinical trial -- Smoking, Nicotine and Pregnancy (SNAP) trial -- will investigate whether nicotine replacement therapy (NRT) is safe, effective and cost-effective for mothers-to-be who want to give up smoking. It will also study the effect on the behavior and development of the child.

Smoking during pregnancy is recognized as a major public health problem.

Around 30% of pregnant women smoke and researchers say it can cause significant health problems in the unborn child. It accounts for around 4000 fetal deaths (including miscarriages) every year and it can lead to premature births, low birth weight, cot death and asthma. It is also associated with attention deficit and learning problems in childhood.

The trial, funded by the British National Institute for Health Research's Health Technology Assessment Program, is being led by Dr Tim Coleman from the Division of Primary Care at The University of Nottingham. He says women are highly motivated to stop smoking when they are pregnant.

If the SNAP trial establishes that NRT is effective and safe when used for smoking cessation by pregnant women, then greater use of NRT by pregnant smokers could have a substantial impact on their health and also on the health of their babies, Coleman said.

Women who report to hospitals for pre-natal ultrasound scans at between 12 and 24 weeks pregnant are being offered trial participation. If they agree to take part they will receive either nicotine or placebo patches. This will be backed up with support and advice on how to deal with cravings, and what to do to avoid smoking. Their progress will be followed until their children are two years old when infants' cognitive development and respiratory symptoms will be compared.

Smoking brings the unborn child into contact not just with nicotine but with a long list of other harmful chemicals. Although there is expert consensus that NRT is probably safer than smoking the team has received funding to establish whether or not this is actually the case.

NRT can double a non-pregnant smoker's chance of giving up, but as pregnant women metabolize nicotine a lot faster than other people it cannot be assumed that NRT will work for them and the SNAP trial will establish whether this is the case.