Anew study found that the rates of pregnancy-related death in the U.S. increased by nearly 28% between 2018 and 2022, with large disparities based on state, race, and ethnicity.

The study, published in JAMA Network Open on April 9, analyzed four years of nationwide data from the U.S. Centers for Disease Control and Prevention. Researchers found that there were 6,283 pregnancy-related deaths during that time. The study determined that the rate increased from 25.3 pregnancy-related deaths per 100,000 live births in 2018 to a peak of 44.1 in 2021, before dropping slightly to 32.6 in 2022. The increase occurred across all the age groups that researchers analyzed, but people between the ages of 25 and 39 experienced the highest increase, according to the study.

The study didn’t investigate why the rates of pregnancy-related death increased over the four-year period. But researchers noted in the study that the COVID-19 pandemic could have had an impact on maternal health and the health care system at large, particularly in 2021.

Dr. Rose Molina, one of the study’s authors and an ob-gyn at Beth Israel Deaconess Medical Center, says she and her colleagues observed “a large variation by state” in the rates of pregnancy-related death. Alabama had the highest at 59.7 deaths per 100,000 live births, followed by Mississippi at 58.2. Meanwhile, California had the lowest rate at 18.5 deaths per 100,000 live births, followed by Minnesota at 19.1. Molina says some explanations for the disparities could be variation in access to prenatal, labor and delivery, and postpartum care, as well as in state Medicaid coverage.

“There really shouldn’t be this level of variation across the states, and we need to do better across all the states,” Molina says. “One of the points we made in that article was that if all states could have performed as well as the highest performing state, like California, we could have avoided 2,679 pregnancy-related deaths” in that four-year period.