Avoiding alcohol while pregnant is safest

Experts warn against any level of alcohol during pregnancy following a review of research. (AAP)

Australian experts are warning against drinking any level of alcohol during pregnancy, even just one drink.

Australian experts are warning against drinking any alcohol during pregnancy, despite a UK study concluding there's not enough evidence to suggest an occasional beverage is harmful to the baby.

A systematic review of all available research on the impact of low level drinking in pregnancy found an association between light drinking and smaller babies at birth. But there was no evidence of other harms, including miscarriage, birth defects and developmental delay.

The review, published in the journal BMJ Open, included experts from the University of Bristol and University Hospitals Bristol NHS Foundation Trust.

They trawled all available research on the effects of light drinking (up to four units of alcohol per week) in pregnancy.

From 26 studies, the team found that drinking up to four units a week while pregnant, on average, was associated with an eight per cent higher risk of having a small baby compared with drinking no alcohol.

But they said while there was an association, this did not prove a direct cause of smaller babies at birth.

The researchers said that overall there was insufficient data to "make robust conclusions", adding that evidence on the effects of light drinking was "sparse".

Australian expert Elizabeth Elliot AM, Professor of Paediatrics and Child Health at the University of Sydney and co-director of the NHMRC Centre of Excellence in Fetal Alcohol Spectrum Disorder, disagrees with the conclusion.

Professor Elliot says there is a paucity of evidence of harm in offspring exposed to low levels of alcohol, but just because we can't see damage doesn't mean there is no damage.

"Even though there may be not obvious risk from low levels of alcohol our advice as health professionals must be the safest option is to avoid alcohol," Prof Elliot said.

"We know that alcohol can cause harm both at a cellular level and a clinical level therefore the precautionary approach is safest and one of the reasons is that often people who are given the go-ahead to drink will drink more than they are advised to drink."

Professor Jane Halliday from the Murdoch Children's Research Institute said the study had its limitations, but the message that low level drinking in pregnancy is OK is ill-advised and national guidelines should not change.

"We recently published a paper that shows that even low amounts of alcohol consumed in trimester one contribute to facial shape in one-year-olds," Prof Halliday said.

The impact on facial shape, published in journal JAMA Pediatrics, were not visible to the naked eye and only seen by using sophisticated 3D facial shape analysis

Despite this, the slight changes are still significant because children who have been exposed to high levels of alcohol in pregnancy have a "very classic face", Prof Halliday said.

"What we were seeing was very subtle manifestations of those differences in the middle of the face."