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.
There are different views on how much alcohol - if any - is safe to drink while pregnantHow much alcohol can you drink while pregnant?
In response, the scientists systematically studied numerous data sets from various eminent observational studies on the effect of light alcohol consumption (2 units up to twice a week, or 4 units a week, approximately equal to 32 grams) compared with consuming no alcohol at all.
The researchers conducted a systematic review and analysis of 5,000 studies published between 1950 and July 2016 based on low alcohol consumption and pregnancy.
It is hoped the findings will help pregnant women make an informed choice about alcohol. By comparison, light or moderate smoking less than 20 cigarettes per day was associated with a 22 percent increased risk.
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 question is light drinking is good or not. "This review confirmed some increased risk of babies being born SGA but little direct evidence of any other detrimental effect for maternal drinking up to 32g/week".
Very few studies compared light to non-drinkers and there was a distinct lack of evidence on most other outcomes for the baby, including development, behaviour, cognitive impairment, greater problems in pregnancy or a more complicated delivery.
At the same time it indicated that consumption should be restricted to within "one to two United Kingdom units, once or twice a week".
But a new review of several existing studies hints that small amounts of alcohol may slightly boost the risk of premature birth and low birth weight.
Researchers found that drinking even small amounts during pregnancy may be linked with higher chances of having a small baby and delivering prematurely.
They added: "However, describing the paucity of current research and explaining that "absence of evidence is not evidence of absence", appears warranted".
"My advice to women is that it's best not to drink at all if you're trying for a baby or are pregnant", said Russell Viner, a professor at the Royal College of Paediatrics and Child Health.
"Formulating guidance on the basis of the current evidence is challenging". It has been hard to associate low levels of alcohol intake in pregnancy and harm, and this work confirms this.
Despite research, experts are still unsure how much alcohol - if any - is safe to drink while pregnant.