Alcohol in pregnancy: do we know how little is too much?
Consuming even small amounts of alcohol in pregnancy may be linked with higher chances of having a small baby and delivering prematurely, researchers have found. But they found very few studies investigating light drinking during pregnancy.
The Department of Health released new guidelines on alcohol consumption during pregnancy in January 2016. They state that no level of alcohol is safe to drink during pregnancy. This is based on the precautionary principle, which assumes potential harm to the foetus in the absence of high quality evidence.
The previous UK guidelines advised women to avoid drinking alcohol while trying to conceive and in the first trimester. But they also indicated that women should not consume more than one to two units, once or twice a week. Two units of alcohol are equivalent to one pint of beer or a medium glass of white wine.
The previous guidance, seemingly ‘permitting’ light drinking, was confusing for health professionals and pregnant women, leading to inconsistent advice.
Earlier reviews have reported on a range of low to moderate alcohol consumption levels in pregnancy but haven’t focussed on the threshold referred to in the previous UK guidelines. So the research team set out to find what evidence exists.
What was the aim of the project?
We aimed to find out what is known about the effects of light prenatal alcohol consumption on pregnancy, including complications, delivery outcomes and measures of growth and development in the children.
Our researchers reviewed all the available evidence, to understand whether the change in the guidelines for pregnant women was backed up by the evidence.
What did we find?
We found very few studies that answered the research question on the specific range of alcohol exposure. The studies we found provided some evidence that even light alcohol consumption in pregnancy is
associated with a small increase in risk of preterm delivery and babies being born small for their gestational age.
We found evidence that women who reported drinking even the small amount of alcohol in the original guidelines were 8 per cent more likely to deliver a small baby, with estimates ranging between a 2 per cent and a 14 per cent increase. The evidence that light drinking affected delivering prematurely was weaker and there was insufficient evidence on other health outcomes.
For most outcomes we found very little evidence to support recommendations that the two units twice a week limit would be safe. This evidence supports the recent change in UK guidelines on alcohol consumption during pregnancy, revised down to 'not drinking at all' and initially only based on a 'better safe than sorry' approach.
The authors however still recommend caution in interpreting these results as the association might not reflect a direct causal link.