Alcohol and pregnancy: is drinking up two units twice a week ‘safe’ or should pregnant women completely abstain?

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 strong beer or a medium size glass (175ml) of light white wine.

The previous guidance, seemingly ‘permitting’ light drinking, was confusing for health professionals and pregnant women, leading to inconsistent advice.

Reviews have reported on a range of low to moderate alcohol consumption levels in pregnancy and haven’t focus on the threshold referred to in the previous UK guidelines. It was therefore necessary to look for evidence supporting either version of the guidelines, to answer the question: “Is there enough evidence to state that drinking up to two units of alcohol up to twice a week during pregnancy is not safe for the unborn baby, and instead mothers should abstain?”.

Project aims

This work 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. The researchers reviewed all the available evidence, to understand whether the change in the Department of Health’s guidelines for pregnant women was backed up by the existing evidence.

What we did

We examined the effects of light alcohol consumption during pregnancy using the best quality evidence available, by systematically reviewing the scientific literature on this topic.

What we found and what this means

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 that we looked at, we found very little evidence to support recommendations that the two units twice a week limit would be safe for the baby. Our work therefore provides further evidence supporting 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.

What next?

We will work on distributing our findings to the public, including pregnant women and those professionals who provide information on alcohol consumption during pregnancy, such as GPs and midwives.

CLAHRC BITE (Brokering Innovation Through Evidence)

Alcohol in pregnancy: do we know how little is too much?

This CLAHRC BITE gives the highlights from this research project in a printable A5 format.

Download the BITE

Links and downloads

Lead collaborators

CLAHRC West staff

Hannah Edwards

Hannah Edwards

Jelena Savovic

Dr Jelena Savović

  • Senior Research Fellow in Evidence Synthesis
  • Evidence
  • Team Lead

Partners on this project

University of Bristol

The University of Bristol is internationally renowned and one of the very best in the UK, due to its outstanding teaching and research, its superb facilities and highly talented students and staff. Its students thrive in a rich academic environment which is informed by world-leading research. It hosts the Elizabeth Blackwell Institute for Health Research.