Heavy alcohol consumption during pregnancy increases the risk of low birth weight, preterm birth and other complications, a new study confirms.

The more heavily a pregnant woman drank each day, the higher the risk of those complications, according to the report, which was published in BJOG: An International Journal of Obstetrics and Gynaecology, that reviewed 36 previous studies.

"This review indicates that any drinking beyond light consumption during pregnancy increases the risks of all three outcomes," said Dr. Jayadeep Patra, a research scientist at the Centre for Addiction and Mental Health in Toronto. 

"It is difficult to know how many units of alcohol there are in a glass, so the current best advice for women is to abstain from drinking during pregnancy."

The risk of low birth weight and small size increased when mothers consumed more than one drink a day, or about 10 grams of pure alcohol.

Preterm birth showed no effect up to 18 grams of alcohol per day, an average of 1.5 drinks per day, the researchers said.

Low to moderate maternal alcohol consumption is considered on average as one alcoholic drink per day.