It's a question on many pregnant women's minds, particularly after the debate was reignited earlier this summer when new studies suggested it might be okay: Is any amount of alcohol consumption safe during pregnancy?

A new study falls into the "no" category, finding that drinking during pregnancy has lasting effects on children's size. The paper is one of the first to analyze the effects of alcohol exposure in a single group of children over a long period of time.

"Although decades of research have shed light on the negative effects of drinking during pregnancy, many questions remain," author Dr. Colin Carter, an instructor in pediatrics at Harvard Medical School, told The Huffington Post. "This study reveals that growth restriction, a known effect of drinking, occurs before birth and in many cases is permanent."

Carter and his colleagues recruited two groups of pregnant women at a clinic in Cape Town, South Africa; 85 were defined as heavy drinkers, consuming two or more drinks per day or four or more drinks on a single occasion while pregnant. Another 63 women were defined as light drinkers, having less than one drink a day, or abstained from alcohol entirely.

Researchers measured their children's weight, height and head circumference when they were babies, and then again at ages five and nine. Children born to heavy drinkers had lower weight, height and head circumference compared to babies who did not have heavy alcohol exposure during pregnancy. Head-size is an indicator of brain growth, which suggests that children regularly exposed to alcohol during pregnancy could have problems with mental development.

The findings will be published in the November issue of the journal Alcoholism: Clinical & Experimental Research.

"These effects may be detrimental to the children as growth deficits have been shown to be related to other health problems, such as lower IQ," Carter said in a statement. "Furthermore, the effects of alcohol on growth were much more severe if the child had iron deficiency anemia as an infant, a condition that is common in the U.S. and worldwide."

While the notion that alcohol hurts development is certainly nothing new, the new study is notable because of its length.

"What they're writing is not unexpected," Dr. Gene Burkett, a professor of obstetrics and gynecology and interim director of the division of maternal-fetal medicine at the University of Miami Miller School of Medicine told HuffPost.

"The value of the study is the longer follow-up," he continued, "They have shown that these changes persist."

The debate about whether any level of drinking during pregnancy is safe heated up earlier this summer after a series of papers by Danish researchers, published in BJOG: An International Journal of Obstetrics & Gynaecology, found that low to moderate alcohol consumption during pregnancy did not hurt children's intelligence, attention or executive function. In those studies, light consumption was defined as one to four drinks per week. Moderate drinking was defined as five to eight drinks.

But some experts pushed back against the findings.

Christina Chambers, an associate professor in the department of family and preventative medicine at the University of California, San Diego, said in a statement that "although we do not want to alarm women who find out they are pregnant and realize that they have consumed low levels of alcohol before they knew they were pregnant, we emphasize that a 'safe' amount of alcohol that any individual woman can drink while pregnant is impossible to establish."

Likewise, the new study does not directly tackle the question of a threshold at which drinking during pregnancy may be safe and therefore, should not be interpreted as saying that light drinking is safe.

"Other research suggests that a pattern of binge drinking over a sustained period of time is likely the riskiest for fetal alcohol spectrum disorder," Chambers told The Huffington Post. "But individuals vary in susceptibility, so there is no established 'safe' threshold."

Though she said it is not yet clear whether post natal factors might have affected the long-term growth of children monitored in the new study, it does seem to show that growth deficiency is "set up" before they are born.

And that, the experts agree, supports the bottom line that there is no clear, safe level of drinking during pregnancy.

"We do not know how much alcohol will create a problem for a fetus. We have never been able to quantify it," said Burkett. "That's why as OBs, generally, we advise patients not to have alcohol during pregnancy."