Women should decide for themselves if they want to drink small amounts of alcohol in pregnancy, a doctor says.
Some say there is no proven safe limit of consumption
Obstetrician Pat O'Brien said experts should not be making a value judgment, the British Medical Journal reported.
He said there was no evidence that low to moderate drinking caused some of the health problems to the foetus associated with heavy drinking.
The government changed its advice this year to recommend pregnant women abstain from drinking.
The Department of Health's May advice came after research found that under the old guidance - that women should drink no more than two units a week - one in 10 were drinking more than the recommended amount.
However, there is confusion as NHS advisory body, the National Institute for Health and Clinical Excellence, issued draft guidance recently saying it was OK to drink small amounts.
Mr O'Brien, from the Institute for Women's Health in London, said foetal alcohol syndrome, which can cause learning difficulties and other disorders, is serious and is clearly a consequence of drinking heavily.
But, he argued, there is still no evidence that low to moderate alcohol intake in pregnancy has any long-term effects.
Mr O'Brien said: "I'm not trying to argue that low levels of alcohol are definitely safe.
"What I am arguing is that we should respect the autonomy of pregnant women.
"We have a duty to be open and honest with the people we advise.
"Women are entitled to decide for themselves and their babies - some are more risk averse than others and will wish to abstain completely."
Mr O'Brien also said that the ban was likely to lead to women not admitting having drunk alcohol in pregnancy for fear of being judged.
"It is not our role, having acknowledged our lack of evidence in this area, to make a value judgment."
But Dr Vivienne Nathanson, of the British Medical Association, said the safest thing was for women not to drink in pregnancy as research had shown conflicting results.
Dr Nathanson said alcohol can adversely affect the reproductive process in several ways, including infertility, miscarriage, premature deliveries, stillbirth and low birthweight babies.
Countries such as the US, Canada, France, New Zealand, and Australia have adopted the abstinence message.
And Dr Nathanson said given the uncertainty over risks "the only sensible message for women who are pregnant or planning a pregnancy must be complete abstinence from alcohol."