FRIDAY, April 21, 2017 (HealthDay News) -- Signs in stores warning about the harms of drinking during pregnancy appear to work: New research shows boozing by mothers-to-be has declined 11 percent in states that require such postings.

Those states have also seen a drop in extremely premature births (less than 32 weeks' gestation) and very-low-birth-weight babies (less than 3.5 pounds), the study found.

The largest impact of the signs has been among women aged 30 and older, according to the study.

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"The signage is working," said study author Gulcan Cil, a health economist at the University of Oregon.

"Drinking alcohol while pregnant has been an issue that many policies have tried to address over the last few decades. An 11 percent change in the prevalence of drinking is not trivial. It is big enough to show up in the birth outcomes," Cil said in a university news release.

The study can't show a direct cause-and-effect connection. Still, the authors suggest that such signs are an effective, low-cost approach to protect the health of pregnant women and their babies.

"Some people never get exposed to these kinds of educational campaigns," Cil said. "I found that the issue has never been studied and evaluated as a public education program or public awareness program."

The findings stem from an analysis of 1989 to 2010 data from the 23 states and Washington, D.C. that require such signs and a group of states that do not. The researchers also evaluated responses to a national behavioral risk survey that asked about drinking patterns during the previous 30 days.

The study results appear in the May issue of the Journal of Health Economics.

More information

The March of Dimes has more on alcohol and pregnancy.