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.
Many pregnant women drink varying quantities of alcohol, although several guidelines recommend total sobriety.
Scientists at the University of Bristol have reviewed all data from high-quality studies into the impact of light drinking, defined as up to four units a...
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".
"There is a continual attempt, especially in Europe, to show that it is okay to drink quote unquote amounts of alcohol during pregnancy", said Grunebaum. Guidance from the chief medical officer advises women to avoid alcohol completely during pregnancy, but women should have the right to know the paucity of evidence to support this position. Light drinking also appeared to have slightly increased the chances of a premature birth.
But we know a lot less about the potential risks of light or moderate drinking while pregnant.
Overall, the researchers backed this view, saying the lack of evidence of harm was not the same as proof that it is fine to drink.
Infographic on alcohol consumption during pregnancy. Image Credit National Organisation on Fetal Alcohol Syndrome
But again, the NHS say the safest approach is to avoid alcohol while pregnant.
At the same time it indicated that consumption should be restricted to within "one to two United Kingdom units, once or twice a week".
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.
If you are anxious about how much you have been drinking when pregnant, talk to your doctor or midwife.
It also found that drinking up to 32g a week while pregnant was linked to eight percent higher risk of having a smaller baby, as compared to no drinking at all.
The researchers said: "Despite the distinction between light drinking and abstinence being the point of most tension and confusion for health professionals and pregnant women, our extensive review shows that this specific question is not being researched thoroughly enough, if at all". "It is most likely low on the basis of the information we now have, but you can't be promised that and you don't know that".
Drinking during pregnancy remains an issue of great concern as nearly 80 percent of moms-to-be in the United Kingdom, Ireland, New Zealand and Australia drink some amount of alcohol during their pregnancy.
"In addition, there has been no evidence regarding possible benefits of light alcohol consumption versus abstinence".