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Sobering evidence on drinking during pregnancy: do we know how little is too much?

Image of two wine glasses and a remote control

Press release issued: 12 September 2017

New research from the University of Bristol suggests that consuming even small amounts of alcohol in pregnancy may be linked with higher chances of having a small baby and delivering prematurely. However, researchers actually found very few studies investigating light drinking during pregnancy.

The research team reviewed all the high quality scientific studies[1]  they could find on the effects of drinking small amounts of alcohol during pregnancy. Small amounts were defined as 1 to 2 UK units, once or twice a week, the recommended maximum level given in the Department of Health’s previous guidance. Two units of alcohol is equivalent to one pint of strong beer or a medium size glass (175ml) of light white wine.

They looked at the effects on a wide range of health outcomes such as miscarriage, still birth, size at birth, and long term developmental delays, behavioural and cognitive deficits.

The review, published today in BMJ Open, found only seven studies with data on whether consuming small amounts of alcohol in pregnancy affected the size of babies at birth. Based on these studies, Dr Loubaba Mamluk and colleagues found evidence that women who reported drinking even this amount of alcohol were eight per cent more likely to deliver a small baby with estimates ranging between a two 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.

This evidence supports the new guidelines released by the Department of Health in January 2016, which advise women not to drink any alcohol when pregnant or trying to conceive: "the safest approach is not to drink alcohol at all". This was based on a "better safe than sorry" principle, in the absence of strong evidence for or against actual harmful effects of alcohol to the unborn baby.

Drinking large amounts of alcohol is clearly linked to foetal alcohol syndrome (FAS) and increases the risk of miscarriage, premature birth and the baby having a low birth weight.

However, the Bristol authors emphasise that the evidence they have analysed refers to light drinking, that the effects they have found are small, and that overall there is still some uncertainty, for example on how light drinking in pregnancy affects other aspects of the baby’s health.

Another reason to be cautious is that the association might not reflect a direct causal link. Women can use this new information to inform their choices, and if they want to avoid any risk from alcohol drinking in pregnancy or when trying to conceive they should avoid all alcohol as a precaution.

According to Dr Luisa Zuccolo, who co-led the study: "Formulating advice on the basis of the current evidence is challenging because we are still building the full picture of what happens to the unborn baby when small amounts of alcohol reach the bloodstream or brain. We wanted to give women the most up-to-date and reliable evidence in order to empower them to make an informed decision about drinking during pregnancy and balancing any possible risk with other factors in their lives."

This research was funded by the National Institute for Health Research (NIHR) through the Collaboration for Leadership in Applied Health Research and Care West (CLAHRC West) and UK Medical Research Council through the MRC Integrative Epidemiology Unit at the University of Bristol.


'Low alcohol consumption and pregnancy and childhood outcomes: time to change guidelines indicating apparently ‘safe’ levels of alcohol during pregnancy? A systematic review and meta-analyses' by Loubaba Mamluk et al is published in BMJ Open

Further information

[1] This was defined as studies of pregnant women or women trying to conceive with prospective assessment of prenatal alcohol exposure (i.e. before birth), sampled from general population. 

About the National Institute for Health Research
The National Institute for Health Research (NIHR): improving the health and wealth of the nation through research.

Established by the Department of Health, the NIHR:

·     funds high quality research to improve health;
·     trains and supports health researchers;
·     provides world-class research facilities;
·     works with the life sciences industry and charities to benefit all;
·     involves patients and the public at every step.

For further information, visit the NIHR website

The NIHR Collaboration for Leadership in Applied Health Research and Care West (NIHR CLAHRC West) works with its partner organisations, including local NHS and public health providers, to conduct applied health research and implement research evidence, to improve health and healthcare across the West. It undertakes applied health research projects, in collaboration with its partners across the region and nationally. The research it does must have a real-world application and fall into one of our broad thematic areas of ‘improving the management of chronic health conditions’ and ‘public health interventions and population health’.

About the MRC Integrative Epidemiology Unit
The Medical Research Council Integrative Epidemiology Unit at the University of Bristol (MRC IEU) conducts some of the UK's most advanced population health science research. It uses genetics, population data and experimental interventions to look for the underlying causes of chronic disease.

The unit brings together an innovative collection of research programmes underpinned by core research activities. Training, public engagement and communication of research findings are cornerstones of our activities.

Substantial investment from both the UK Medical Research Council and the University of Bristol provides resources, research support and infrastructure to world-leading, multidisciplinary research in a vibrant and forward-looking environment.

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