The study, published Tuesday in the Journal of the American Medical Association, observed a sample of pregnant women in the state.
Pot use among the study subjects climbed from 4.2 percent to 7.1 percent from 2009 through 2016.
One expert speculates that the rise might be partially explained by the increased availability of legal marijuana in recent years.
According to the Centers for Disease Control, doctors caution that marijuana's effects on a fetus aren't clear, but could include low birth weight and developmental problems.