A new study concludes that drinking and pregnancy are not a healthy mix. There’s still disagreement over how much is too much.

Is “just one drink” too much if you’re expecting?

While opinions differ, a new study in BMJ Open found that even small amounts of alcohol can do harm to a fetus.

Lead researcher Luisa Zuccolo, a health epidemiologist at the University of Bristol, looked at drinking once or twice a week versus abstaining completely.

Her team reports that drinking up to 2 to 3 drinks was linked to a 10 percent higher risk of preterm delivery.

Her team couldn’t say if that increased risk is caused by alcohol or other factors.

Pregnant women should be advised to abstain, the researchers said, but that recommendation should note a lack of evidence showing a “clear detrimental effect, or safe limit, of light alcohol consumption on outcomes.”

Last year, the Centers for Disease Control and Prevention (CDC) advised that women of childbearing age shouldn’t drink alcohol unless they’re taking birth control.

That advisory drew widespread criticism.

“Alcohol can permanently harm a developing baby before a woman knows she is pregnant,” CDC Principal Deputy Director Dr. Anne Schuchat said in a statement. “About half of all pregnancies in the United States are unplanned, and even if planned, most women won’t know they are pregnant for the first month or so, when they might still be drinking. The risk is real. Why take the chance?”

A 2015 CDC survey found that 10 percent of expectant American women had at least 1 alcoholic beverage during the span of 1 month.

Dr. Susan Astley, director of the Washington State Fetal Alcohol Diagnostic and Prevention Network and a professor at the University of Washington, noted that 1 out of every 7 children with fetal alcohol syndrome were exposed to 1–8 drinks a week while their mothers were pregnant.

Genetics also play a role.

The risk is not only based on how much alcohol a mother consumes. No two fetuses are equally vulnerable to the adverse effects of alcohol, she noted.

“The message to women is simple: When a pregnant woman drinks, her child is at risk. If she drinks heavily, her child is at higher risk,” Astley told Healthline.

To ensure the healthiest baby possible, women shouldn’t drink alcohol when trying to conceive or when they are pregnant. Those having a hard time trying to stop drinking should seek help.

“The only safe amount to drink, for all fetuses, is none at all,” Astley added.

Dr. Amos Grünebaum, a professor and director of obstetrics, as well as chief of labor and delivery at Weill Cornell Medicine in New York City, told Healthline that the new study confirms the fact that even small amounts of alcohol can cause harm to a baby.

“Pregnant women are always reminded to eat healthy food and to stay away from anything that can potentially harm the baby. Alcohol has zero nutritional value so there is no question why it shouldn’t be used in pregnancy,” he noted.

The common notion that Europeans drink regularly during pregnancy and it is safe is not true, he contended.

“Europeans do it all the time and many babies in Europe are born with fetal alcohol syndrome (FAS). In fact, some European countries have among the highest incidence of FAS worldwide,” Grünebaum said.

“Alcohol is a poison, no matter how you look at it,” he explained. “There is no safe amount for any pregnant women to drink because it is different from one person to another. The only safe amount is to not drink alcohol at all in pregnancy.”

“We don’t encourage smoking tobacco, heroin, cocaine, or marijuana use in pregnancy, and alcohol is potentially worse,” he added.