How much alcohol can a pregnant woman safely drink? It’s a question many expectant mothers ask their OB/GYN. But the truth is, no one is really sure. New research investigating—once again— the effects of light drinking during pregnancy found little evidence to support or debunk the danger of low alcohol consumption on the developing fetus. According to experts, the uncertainty, and potential for harm, means that it is still best to go without a drink until after giving birth.

The new study, an open-access report published online in BMJ Open, reviewed 26 studies on the effects of low alcohol consumption at 32 and fewer weeks of pregnancy. The researchers found very little evidence to make a definitive conclusion on how much women can safely drink during pregnancy. The study did find that low alcohol consumption can lead to small gestational size and preterm delivery, two traits that may lead to other health problems later in life. For this reason, the team concluded that expectant mothers should steer clear from any amount of alcohol during their pregnancies.

“Due to the limited number of studies investigating low alcohol consumption and due to a link found between this amount of alcohol (up 32 grams per week) and having a small-sized baby (small for gestational age), we advise women to abstain from alcohol consumption during pregnancy as per the UK guidelines,” study co-author Loubaba Mamluk told Newsweek in an email.

But quantity still remains a matter of debate. Heavy drinking is not advised for anyone and can be especially dangerous for pregnant women because it may lead to a serious birth defects, such as fetal alcohol syndrome. How light alcohol exposure may affect a developing fetus is less clear. Some reports have suggested that there may be “safe” drinking levels for pregnancy.

For example, a 2013 study from the University of Bristol in the U.K., also published in BMJ Open, followed 6,915 children whose mothers had between none to moderate amounts of alcohol during pregnancy. The analysis, which tracked the health of these children from birth to age 10, concluded that light to moderate drinking during pregnancy had “no effect” on any children involved in the research. The researchers even found that children born to mothers who drank light amounts of alcohol during pregnancy had better outcomes than those born to mothers who completely abstained.

Still, most experts agree that even a small risk is still a serious risk when it comes to a child’s health.

Dr. Amos Grunebaum, chief of labor and delivery at New York-Presbyterian Hospital and professor at Weill Cornell Medicine, who was not involved with this research, told Newsweek that he completely agrees with the study’s findings.

“There is no safe amount for any pregnant women to drink because it is different from one person to another,” Grunebaum told Newsweek. “The only safe amount is to not drink alcohol at all.”

As for other research that suggests low amounts of alcohol have zero effect on pregnancy, Grunebaum says these assertions may be an attempt to make drinking certain amounts socially acceptable in some countries.

“There is a continual attempt, especially in Europe, to show that it is okay to drink quote unquote amounts of alcohol during pregnancy,” said Grunebaum. “Some people feel alcohol is something that is normal, but drinking alcohol even in small amounts does not do anything good.”

Ultimately, the verdict is still split on the effects of light drinking during pregnancy. And due to the difficult nature of studying this topic, we may never know for sure where the line is drawn between safe and unsafe drinking during pregnancy.