13 September, 2017
Researchers can't ethically do a true study to determine exactly how much alcohol a pregnant person can drink before it crosses the line and hurts the fetus, so there's no evidence there, either. Different doctors might have contradictory opinions; while some recommend avoiding alcohol completely, others are a bit more lenient.
Last year Dame Sally Davies, the chief medical officer, issued fresh guidance on alcohol, saying: "Although the risk of harm to the baby is low if [mothers] have drunk small amounts of alcohol before becoming aware of the pregnancy, there is no "safe" level of alcohol to drink when you are pregnant".
The new paper included a systematic review and analysis of previous studies on low alcohol consumption and pregnancy that were published between 1950 and July 2016.
For most of the consequences the researchers analyzed, there were only a few observational studies that compared light to non-alcohol consumption.
Andrew Shennan, professor of obstetrics at King's College London, said: "The association of alcohol in excess with adverse outcomes is well established, including in pregnancy". However, women should still avoid alcohol during pregnancy, just to make sure they don't experience any unpleasant events. Light drinking also appeared to have slightly increased the chances of a premature birth.
The lack of high quality data illustrates the difficulties of designing research that can truly evaluate the causal impact of light drinking while minimising the risks of bias and confounding, say the researchers.
Without the evidence, it is impossible to say whether drinking small amounts is safe or not, they say.
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In seven of those studies, light drinking was associated with at least eight percent increased risk of having a small baby or a premature birth. But women who do drink small amounts during their pregnancy can be reassured that they are not likely to have caused any danger to their baby's health.
The evidence on how much, if any, is safe to drink, or at what stages of pregnancy, is notable by its absence, they add. "Formulating guidance on the basis of the current evidence is challenging", she said, according to the New York Post.
As there is no clear advice on whether pregnant women can drink, there is no established safe limit on the amount of units they can consume.
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.
Dr. Janet Williams, professor of pediatrics at the University of Texas Health San Antonio, who served as one of the lead authors on a 2015 American academy of pediatrics advising no alcohol during pregnancy.
During the nine months of pregnancy, many pregnant women have wondered - would one or two glasses of wine really put my baby at risk?