A year ago new guidance to the NHS in England urged women to try not to drink at all, but in the real world, say the new study's authors, up to 80% in the UK, Ireland, New Zealand and Australia drink some alcohol while they are pregnant.
"When a woman drinks alcohol during pregnancy, the alcohol in her blood quickly passes through the placenta and the umbilical cord to the baby", Jarris explained.
United Kingdom researchers reviewed all studies done on the subject since the 1950s and found no hard proof that one or two glasses of wine a week (four units) poses a threat to the child.
But the evidence on how much, if any, is safe to drink, or at what stages of pregnancy, is notable by its absence.
It added: "This issue remains of great public health importance, with alcohol consumption during pregnancy prevalent in the UK, Ireland, New Zealand and Australia with up to 80% of women consuming some alcohol during pregnancy".
Likewise drinking up to four units or 32g a week was associated with an 10 percent increased risk of premature birth.
Professor Jane Halliday from the Murdoch Children's Research Institute says the study has its limitations but the message that low level drinking in pregnancy is OK is ill-advised.
The study noted in comparison, light to moderate smoking of less than 20 cigarettes per day was associated with a 22 percent increased risk.
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.
"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". They found an eight per cent risk of smaller babies among the women who drank, but said this wasn't enough for a "robust conclusion".
Researchers found that drinking even small amounts during pregnancy may be linked with higher chances of having a small baby and delivering prematurely.
The UK's Chief Medical Officer commissioned the review into alcohol's effect on pregnancy because of how much "tension and confusion" the matter sparks between health professionals and women who are with child. "Formulating guidance on the basis of the current evidence is challenging", she said, according to the New York Post. "We believe women should have access to high quality, evidence-based information on matters relating to pregnancy, are capable of making the choices that are right for them, and should be trusted to do so".
"These were all representative studies of pregnant women or women trying to conceive who reported on their alcohol use before the baby was born", Mamluk said. It also shows the failure of researchers so far to focus on light versus no alcohol consumption instead of moderate and heavy alcohol consumption.