While many health organizations strongly advise against drinking while pregnant - the American Academy of Pediatrics says no amount should be considered safe - some controversial studies previously have suggested that light drinking might not be harmful for the baby's future health.
The researchers took a close look at studies that involved drinking up to 32 grams of alcohol per week, equivalent to about two pints of beer or two glasses of wine, Mamluk said.
The study, published in the journal BMJ Open, found an 8 per cent higher risk of smaller babies among women who drank four units a week - insufficient for a "robust conclusion".
A spokeswoman for the British Pregnancy Advisory Service (BPAS) said: "What seems to lie at the heart of public messages addressing alcohol in pregnancy is whether women can be trusted to understand the existing evidence, and whether they are able to recognise the difference between light and heavy drinking".
But they insisted the best advice for pregnant women was to play safe and steer clear of alcohol.More news: Miami woman delivers her own baby during Hurricane Irma
For a question that affects so many people, surprisingly little research has been done, health experts who reviewed the scant evidence said Tuesday.
The advice backs the guidelines from the HSE, which recommends abstinence.
According to the authors, up to 80% of mothers-to-be in Britain, Ireland, New Zealand and Australia drink some alcohol while pregnant.
Strict government guidelines warning pregnant women against drinking any alcohol are not justified by evidence, a landmark study has found.
'As the evidence is uncertain, the lowest risk approach is to avoid alcohol'. From among almost 5,000 articles, it selected 26 relevant studies with data suitable to be pooled.More news: National Football League files appeal of Elliott's preliminary injunction
For instance, "women often ask about "safe" levels of drinking during pregnancy - 'but one glass is OK, isn't it?'" Loubaba Mamluk, senior research associate in epidemiology at the University of Bristol in the United Kingdom and lead author of the paper, said in an email.
"We were surprised that this very important topic was not researched as widely as expected", she said.
The analysis showed that drinking three standard drinks, totalling 32g of alcohol a week, was associated with an 8pc higher risk of having a small baby, compared with drinking no alcohol at all.
James Nicholls, research director at the charity Alcohol Research UK, said the findings "should caution us not to create a situation where mothers-to-be are made more anxious, or subject to unnecessary moral judgment, on the issue of very light alcohol consumption".
But the Bristol team emphasised that their review, which was funded by the National Institute for Health Research, referred to light drinking and that the effects they found were small.More news: What happened to Hurricane Jose?
"A precautionary approach is still reasonable, but with luck this should dispel any guilt and anxiety felt by women who have an occasional glass of wine while they are pregnant".
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