Emma Haughton reports on the hazards of cigarettes and the abuse of alcohol
One of the most wearisome and worrying aspects of pregnancy can be the constant stream of admonitions and advice you receive about how to protect your unborn child. The list of forbidden pleasures seems to grow daily: beer, Brie and beef are amongst many things that are out of bounds for those nine long months - or longer if you breastfeed.

The good news when it comes to alcohol is that a little is probably still alright. So when you get that invitation to a party, you don't have to sit on the sidelines clutching an orange juice.

There have been studies into the effects of drinking alcohol during pregnancy and it is known that alcohol does affect your ability to conceive, as well as the chances of miscarriage and the development of your baby. Getting drunk can be particularly damaging. However, one or two units once or twice a week is unlikely to cause you or your baby any harm. This advice for pregnant women is not new but was recently backed up by a review of scientific evidence by an expert committee which reported to the Government's sensible drinking review published last December.

One study published since then has come up with a surprising finding. Professor Jean Golding, professor of paediatrics at Bristol University who led the study of 15,000 pregnant women in Avon said: "We found a U- shaped curve where women who had never drunk alcohol during pregnancy were more likely to have a low birth weight than those who drank occasionally." However, as Golding and her team acknowledge, there is no explanation for this.

"Confusion amongst mothers about this comes as no surprise to the HEA which is often asked for advice," says Sarah Harris of the HEA's Alcohol project. "So we went out and asked pregnant women what information they would find most useful. The things they told us have been used to develop a new leaflet which will be available shortly from GP's and health centres."

Advice on smoking is much more cut and dried: don't. The wealth of research around smoking and pregnancy shows links with reduced fertility in women, up to a four-fold risk of ectopic pregnancy, a higher risk of miscarriage and stillbirth, and an average 200g lower birthweight in exposed babies. The Foundation for the Study of Infant Deaths warns that maternal smoking during pregnancy quadruples the risk of cot death, while the Avon study found that smoking mothers have increased problems during pregnancy, including vomiting, thrush and urinary tract infections.

"Our research also shows that smoking in pregnancy has a major impact on the development of babies, making them more likely suffer from wheeziness and to develop asthma," says Golding, who believes these effects may be permanent. "If the lungs start off being underdeveloped, it is unlikely they will catch up. You are creating a vulnerable child."

Quitting during pregnancy is a positive move that should be continued after the birth; studies show the risk of cot death, respiratory illness and asthma are heightened in babies exposed to passive smoking by parents. Smoking also makes breastfeeding more difficult and reduces the nutrient levels in the milk.

Most sinister, perhaps, is Golding's suspicion that smoking alters a woman's hormonal profile, prompting an earlier menopause and increased risk of conditions like the bone-thinning disease osteoporosis. She in concerned that these abnormal levels of sex hormones in the mother may also cause changes to the sexual development of her children. Female babies born to pregnant rats exposed to tobacco smoke, for instance, have atrophied ovaries, while data from the 1958 National Child Development Study suggests that boys born to smoking mothers were significantly more likely to have undescended testes.

Despite the fact that 90 per cent of women are aware that smoking during pregnancy puts their baby at risk, only a quarter successfully give up just before or when they get pregnant, although 40 per cent do cut down. However, the HEA emphasises that it's never too late to minimise the dangers. Those who do quit can increase the chance of healthy birthweight, cut the risk of having a premature baby by half, and reduce the risk of stillbirth by a third.

If you need free and helpful advice on quitting smoking, you can telephone the Quitline on 0800 00 22 00.