Unaware of health issues, four out of five expectant mothers drink in Australia.
The survey analysed the drinking habits of more than 1200 young mothers as part of a major longitudinal study.
While most pregnant mothers had a low alcohol intake, one out of every five drank averagely, and some drank heavily, the study found.
Gap in research and changes in official guidelines over the years saw many women choose to drink during pregnancy though typically at low levels, said Powers.
"While it's totally clear a lot of alcohol is bad for the baby. There is no evidence of harm for small amounts of alcohol, but neither is there evidence there's no harm," News.com.au quoted Powers as saying.
2001 guidelines recommended a low intake from zero alcohol and then it came back to no alcohol again in 2009. This confused women and health practitioners.
"It is important that the large group of women who drink alcohol at low to moderate levels receive clear and consistent messages from health professionals," said Powers.
The research was published in the Medical Journal of Australia.