Relatively few women in the study -- 13% -- had a baby with fetal growth restriction. Greater caffeine consumption was linked to greater odds of having a baby with fetal growth restriction.
For instance, compared to women who got less than 100 milligrams per day of caffeine, the odds of having a baby with fetal growth restriction were:
20% higher for women who got 100-199 milligrams per day of caffeine
50% higher for women who got 200-299 milligrams per day of caffeine
40% higher for women who got more than 300 milligrams per day of caffeine
For comparison, a standard 8-ounce cup of drip coffee has 85 milligrams of caffeine.
The researchers -- who included Justin Konje, MD, of England's University of Leicester -- calculated those estimates after considering the women's alcohol and tobacco use.
The findings don't prove that caffeine was to blame for fetal growth restriction. But Konje and colleagues point out that caffeine can cross the placenta, passing from mother to fetus.
The issue might not be caffeine itself, but one of the compounds that caffeine breaks down into, Konje's team speculates.
Caffeine During Pregnancy: Second Opinion
Not all studies on the topic have tied caffeine consumption to increased risk of fetal growth restriction, so an editorial published with the study stops short of telling pregnant women to quit caffeine.
"We think that this advice is not justified by the current body of evidence, and that such advice may unnecessarily frighten women who have consumed caffeine while pregnant," write the editorialists, who included Professor Jorn Olsen, MD, PhD, of the University of California, Los Angeles School of Public Health.
But Olsen's team isn't dismissing the potential risk.
"We ... think that pregnant women should be advised to reduce their intake of caffeine products during pregnancy," as long as they don't replace those products with alcoholic beverages or sugary soft drinks, Olsen and colleagues write.