Researchers have found that low to moderate alcohol use by pregnant patients may contribute to subtle changes in their babies' prenatal development.

The study was published in the journal Alcohol Clinical and Experimental Research. "In exploratory analyses, the effect on gestational age was more pronounced in male infants, and for birth length, it was stronger in females," Bakhireva said.

She cautioned that these effects should be interpreted with caution because of the study's limited statistical power to conduct sex-specific analyses and the challenges of accounting for other contributing factors.

There is a good deal of research on the prenatal effects of heavy alcohol use, usually defined as 14 drinks per week, or binge drinking, defined as four drinks or more per occasion, Bakhireva said.

"We know quite a bit from these earlier studies of heavy alcohol use about the effect on prenatal outcomes, especially preterm delivery and growth restriction, as well as neurodevelopmental outcomes, but we specifically focused on more moderate alcohol exposure because it's much more prevalent," she said.

Early pregnancy is a critical period for the formation of organs in the developing fetus, making it a particularly vulnerable window for alcohol exposure, Bakhireva said.

"Almost everybody drinks before they know they are pregnant, and risky drinking before pregnancy is predictive of drinking later on," she said. "That's a unique aspect of the study. We carefully looked at the patterns of drinking around conception and early pregnancy."

Most of the participants substantially reduced their drinking or stopped altogether once they learned they were pregnant, Bakhireva said. Even with reduced alcohol, there were some deficits seen in both male and female infants, however.

She emphasises that larger studies that combine samples across the country are needed to replicate the findings and examine sex-specific effects further.