The U.S. infant mortality rate rose 3% last year — the largest increase in two decades, according to the Centers for Disease Control and Prevention.

White and Native American infants, infant boys and babies born at 37 weeks or earlier had significant death rate increases. The CDC's report, published Wednesday, also noted larger increases for two of the leading causes of infant deaths — maternal complications and bacterial meningitis.

"It's definitely concerning, given that it's going in the opposite direction from what it has been," said Marie Thoma, a University of Maryland researcher who studies maternal and infant mortality.