Perth researchers have found no link between low and moderate alcohol consumption and alcohol-related birth defects, but those who drank heavily during their first trimester had a four-times greater chance of having children with birth defects.
More than 4714 non-Aboriginal women were surveyed three months after they'd given birth to live babies in WA hospitals between 1995 and 1997, to determine their levels of alcohol consumption during pregnancy.
The Telethon Institute for Child Health Research study, published in US online journal Paediatrics, classified heavy drinking as consuming more than seven standard drinks in a week and binging on more than five alcoholic beverages in a session, more than once a week.
A standard drink contains 10 grams of alcohol, which equates to 100 millilitres of wine.
Only 40 per cent of women abstained from drinking throughout their entire pregnancy, while 16 per cent of those who refused alcohol in their first trimester drank in later trimesters.
The study found 306 children suffered from a variety of birth defects, while 51 others were diagnosed with defects specifically associated with alcohol consumption.
Mothers who drank heavily during the first trimester were four times more likely to have children with the alcohol-related defects like cardiac, renal and optical problems as well as skeletal abnormalities and congenital deafness.
Ventricular septal defects, where a hole is found between the right and left ventricles of the heart, were the most commonly diagnosed, and atrial septal defects, where the wall that separates the upper and lower heart chambers does not close completely, followed.
Women who had less than seven standard drinks a week and no more than two in a day were considered to have low drinking levels and mothers who binged on more than 50 grams of alcohol during sessions less than weekly and consumed seven standard drinks a week were moderate drinkers.
Study author Colleen O'Leary said the analysis showed no link between low alcohol exposure during pregnancy and birth defects.
"While this finding may provide some reassurance to mothers who unknowingly consumed alcohol before they knew they were pregnant, the best advice is still to follow the national guidelines that advise expecting mums to avoid alcohol in pregnancy," Dr O'Leary said.
Dr O'Leary said health professionals needed to discuss alcohol use with women who were pregnant or of childbearing age because nearly half the women in the study had unplanned pregnancies, increasing the risk of the foetus' exposure to alcohol.
"This means that prevention strategies will need to target not only pregnant women but also drinking at harmful levels and unplanned pregnancies among all women of child bearing age," Dr O'Leary said.
She cautioned that not all birth defects associated with alcohol were present in children who took part in the study and that women who abstained from drinking also had children with traditionally alcohol-related birth defects.