Texas has seen an “unusual,” dramatic increase in the number of women who died from pregnancy-related causes in the last five years, according to a new study.

The state’s rate of maternal mortality nearly doubled between 2010 and 2014, according to research published by the medical journal Obstetrics and Gynecology. Although maternal mortality rates are up nationwide, no other state experienced such a sharp rise, the study’s authors found.

The researchers, led by Marian MacDorman, a professor at the University of Maryland Population Research Center, found that between 2000 and 2010, Texas saw only a “modest increase” in maternal mortality, from 17.7 to 18.6 deaths per 100,000 live births.

The next year, Texas’ rate spiked, to 33 deaths per 100,000 live births, reaching “levels not seen in other U.S. states,” according to the study. That stood in sharp contrast with California, a state with a comparable population that has seen a steady decline in its maternal mortality rate over the last decade.

“There is a need to redouble efforts to prevent maternal deaths and improve maternity care for the 4 million U.S. women giving birth each year,” the authors wrote.

Scientists define maternal mortality as the death of a woman while pregnant or within 42 days of the termination of her pregnancy, not including deaths by accidental causes.

In 2012, 148 women in Texas died from pregnancy-related complications, including excessive bleeding, obesity-related heart problems and infection. Two years before, 72 women died from those causes.

The study examined maternal mortality rates across the country, and researchers said they could not explain the specific, sudden growth in the number of deaths in Texas.

The study mentioned “changes to the provision of women’s health services” — a reference to cuts made by state lawmakers in 2011 that stripped funding from Planned Parenthood and other women’s health and family planning services — but the researchers stopped short of saying whether that policy change had any effect on the numbers.

“Still, in the absence of war, natural disaster, or severe economic upheaval, the doubling of a mortality rate within a two year period in a state with almost 400,000 annual births seems unlikely,” the study’s authors wrote.

Disclosure: Planned Parenthood has been a financial supporter of The Texas Tribune. A complete list of Tribune donors and sponsors can be viewed here.