Study principal investigation Brenda Eskenzi of the University of California, Berkeley, found levels of organophosphate metabolites in the mother's blood when the child was in the womb were significantly linked to attention problems at age 5.
The study, published in the journal Environmental Health Perspectives, also found the effects were stronger among boys.
Eskenzi pointed out a different study by researchers at Harvard University associated exposure to organophosphate pesticides in school-age children with higher rates of attention-deficit hyperactivity symptoms.
"These studies provide a growing body of evidence that organophosphate pesticide exposure can impact human neurodevelopment, particularly among children," Eskenazi said in a statement. "We were especially interested in prenatal exposure because that is the period when a baby's nervous system is developing the most."
Eskenazi and colleagues tracked more than 300 Mexican-American children living in an agricultural community -- participants in the Center for the Health Assessment of Mothers and Children of Salinas, a longitudinal study.