Pregnant teenagers are smoking in the hope of having smaller babies so that childbirth is less painful.
Labour's public health minister Caroline Flint made the claim after discussions with health professionals and young mothers.
"It is important that we understand what stops young women making healthy choices so we can provide the right answers to their concerns," she said. "In this case, childbirth is no less painful if your baby is low weight. So smoking is not the answer, pain relief is."
Miss Flint warned women that the practice was pointless because the commonly-held idea that giving birth to a large baby is more painful is a myth.
Official advice is that women should not smoke at all during pregnancy. Research suggests women who smoke are less likely to carry their babies to full term and there is a 26 per cent increased risk that they will miscarry or experience a stillbirth.
Despite years of anti-smoking initiatives targeting expectant mothers, the number of pregnant smokers has remained high.
 Babies of smoking mothers are an average 7 oz lighter at birth.
Figures show that one in ten women continue to smoke when they are pregnant.
Around 400 babies a year die in the womb or shortly after being born directly because of their mother's nicotine habit.
Women aged 20 or under were more likely to smoke before or during pregnancy than those aged 35 and over.
Royal College of Midwives expert Gail Johnson said there was no evidence that having a smaller baby reduced pain in labour.
"Many midwives offer classes designed specifically to meet the needs of teenagers and challenge their peer group chats about keeping down their weight by smoking rather than healthy eating and exercise. Midwives know how important it is to support pregnant women and they can link with other support agencies to provide advice on smoking cessation. It is vital that the risks associated with smoking are highlighted and that women are then supported to make changes to their lifestyle but the RCM is very clear that there is no evidence that the size of the baby relates to the amount of pain the woman may experience."
Baby charity Tommy's said any mother who smoked during pregnancy was putting her child at unnecessary risk.
Spokesman Charlotte Davies said: "Much research has shown that women who smoke during pregnancy give birth to babies on average 7oz lighter than those born to those who don't. Worryingly, many women are seeing this as a reason to smoke whilst pregnant, as they believe the myth that the lower the birth weight of the baby, the lower the pain level experienced during labour.
However, there is no evidence to show that the level of pain during labour and the weight of the baby are related. Therefore women, not just teenagers, who continue to smoke during pregnancy are putting the health of their baby at unnecessary risk, as smoking is the biggest preventable cause of low birth weight babies in the UK."
October 2006 | 
Abortion Time Limit Cut?
