About 4 percent of women incarcerated in state prisons across the U.S. were pregnant when they were jailed, according to a new study released Thursday that researchers hope will help lawmakers and prisons better consider the health of women behind bars.

The number of imprisoned women has risen dramatically over the past decades, growing even as the overall prison rates decline. But there had been a lack of data on women's health and no system for tracking how frequently incarcerated women were pregnant, or what happened to the pregnancies. The Bureau of Justice Statistics, for example, collects data on deaths in custody but not on births.

Dr. Carolyn Sufrin of Johns Hopkins University School of Medicine attempted to fill the void by collecting data from 22 state prison systems and 26 federal prisons during a yearlong period in 2016 and 2017. She released her results in the American Journal of Public Health .

"The fact that nobody had collected this data before signals just how much this population is neglected," Sufrin said.

Brenda Baker, a professor and researcher at Emory University School of Nursing who teaches prenatal care to pregnant women who are incarcerated in Georgia, said the research was much needed.

"We are so starved for data. The fact that someone can get something like this and share it excites us," she said. "Those of us who do research in this area will use it far and wide."

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