The study, carried out by the Sahlgrenska Institute in Gothenburg, found that women who consumed caffeine in coffee, tea, carbonated drinks and cocoa-based food such as chocolate, were more likely to produce a child with a lower birth weight.
"As the risk for having a low birth weight baby was associated with caffeine consumption, pregnant women might be counselled to reduce their caffeine intake during pregnancy as much as possible," project leader Dr. Verena Sengpiel told the Health Day journal.
"Caffeine consumption is strongly correlated with smoking, which is known to increase the risk for both preterm delivery and the baby being small for its gestational age," she added in a statement.
While the study found no connection with caffeine intake and preterm delivery, researchers found a correlation between caffeine intake and babies being born smaller than expected.
"This association remained even when we corrected for maternal smoking habits and when we only looked at non-smoking mothers, which implies that caffeine itself also is associated with birth weight," she added.
The biggest effect on the gestation period was found to be in the intake of coffee containing caffeine. Women's gestation periods were extended by eight hours for every 100 milligrammes of caffeine they consumed each day.
Just under 60,000 pregnant Norwegian women were observed in the study, which was carried out together with the Norwegian Mother and Child Cohort.