While heavy drinking is clearly harmful to the unborn baby, often leading to miscarriage, premature birth and foetal alcohol syndrome, the possible effects of light drinking have been less clear.High quality data on this issue is lacking due to ethical and methodological issues. On the one hand, experiments (clinical trials) in this area are impossible to conduct. Clinical trials would include randomising a group of pregnant women to drinking alcohol, which is clearly unethical. On the other hand, in observational studies we can never be sure whether the results are due to alcohol or other factors, such as wealth or education.

‘One glass is OK, isn’t it?’

Women often ask about “safe” levels of drinking during pregnancy. The distinction between light drinking and abstinence is indeed the point of most tension and confusion for health professionals and pregnant women, and public health guidance varies worldwide.Our new review of the evidence, published in BMJ Open, shows that this specific question is not being researched thoroughly enough.As there can be no clinical trial research carried out on this topic, we systematically reviewed all the data from a wide range of high quality observational studies. These studies involved pregnant women, or women trying to conceive, who reported on their alcohol use before the baby was born. The researchers assessed the impact of light drinking, compared with no alcohol at all. >> Read MoreSource: The Conversation