Prof. Russell Viner, from the Royal College of Paediatrics and Child Health, said: "My advice to women is that it's best not to drink at all if you're trying for a baby or are pregnant".
Official NHS guidance from the chief medical officers for the United Kingdom published a year ago said expectant mothers should not drink at all because "experts are still unsure exactly how much if any alcohol is completely safe for you to have while you're pregnant".
These include miscarriage, premature birth, undersized babies, and longer-term issues, such as the developmental delays, impaired intellect, and behavioural difficulties typical of fetal alcohol syndrome, the study in the "British Medical Journal Open" revealed.
For most of the consequences the researchers analyzed, there were only a few observational studies that compared light to non-alcohol consumption.
Number of women drinking alcohol is extreme than expected. However, women should still avoid alcohol during pregnancy, just to make sure they don't experience any unpleasant events.
There was also a potential risk linked to premature birth, although this was less clear.
Also, researchers stated that the lack of eminent data shows the complications of designing research that can truly estimate the causal effect of light alcohol consumption while minimizing the risks of bias and confounding. However, a new study suggests light drinking might not be that unsafe.
The study went on to say that the "distinction between light drinking and abstinence" has been "the point of most tension and confusion for health professionals and pregnant women" and has contributed to "inconsistent guidance and advice now and in the past".
From 26 studies, the team found that drinking up to four units a week while pregnant, on average, was associated with an 8% higher risk of having a small baby compared with drinking no alcohol, with a range across the studies from 2% to 14%.
A clinical trial showed that women with at-risk drinking have more chances to reduce their consumption if they were warned of the risks for their pregnancy and their unborn child on several occasions than if they were simply given an information brochure.
If you are anxious about how much you have been drinking when pregnant, talk to your doctor or midwife. Therefore, all doctors tell women to avoid drinking high units of alcohol. But they added: "However, describing the paucity of current research and explaining that absence of evidence is not evidence of absence', appears warranted".
"Formulating guidance on the basis of the current evidence is challenging", the study went on. The American Congress of Obstetricians and Gynecologists says that there is "no safe level of alcohol use during pregnancy".
Experts still recommend not drinking any alcohol while pregnant.