Study reports alarming increase in U.S. maternal mortality rates

Mar 20 2024 Northwestern University

The U.S. maternal mortality rate is accelerating at an alarming rate, reports a new study from Northwestern Medicine. But it's not due to the widely believed hypothesis that maternal mortality in the U.S. has increased largely because people are getting pregnant at older ages. 

In fact, the study found maternal mortality increased among every age group. The greatest relative increases among people aged 25 to 29 and 30 to 34 years old, the study found.  A commonly held hypothesis is that more pregnancy-related deaths are occurring because more people are having children later in life, so we wanted to investigate this question. However, we found that's not why we're seeing a spike in the number of maternal deaths. Older maternal age is an important risk factor in maternal mortality, but our findings highlight the need to learn what else is causing these rates to accelerate in more recent years, especially in younger adults less than 35 years old. We're going in the wrong direction." 

Dr. Sadiya Khan, corresponding author, Magerstadt Professor of Cardiovascular Epidemiology and associate professor of cardiology at Northwestern University Feinberg School of Medicine

Between 2014 and 2021, the average U.S. maternal age -; a well-established risk factor for maternal mortality -; increased from 28.3 to 29.4 years old, the study found. In that same period, the overall maternal mortality rates in the U.S. nearly doubled, from 16.5 to 31.8, with the largest increase of 18.9 to 31.8 occurring from 2019 to 2021.

The study was published March 18 in the American Journal of Preventive Medicine.

This is the first study to highlight that age is not a driver in the increasing maternal mortality rates in the U.S. So, what is driving it? 

While this study wasn't able to explore specific causes of death, a large body of prior research, much of it published by Khan, has found cardiovascular disease (hypertensive disorders, heart failure and stroke) is a major contributor to poor maternal health outcomes.  Related StoriesPregnant women with autoimmune conditions at a greater risk of developing adverse pregnancy outcomes, study suggestsMouse models shed light on the effects of metformin use during pregnancy on offspringTeen pregnancy may be associated with risk of premature mortality in early adulthood

"It is critical that we understand what the causes of deaths are and how we can prevent them, as maternal deaths are largely preventable," Khan said. "While some states, like Illinois, have maternal mortality review committees, we also need better national infrastructure and surveillance programs to review and address the root causes of maternal health crisis."  Study only includes states with pregnancy checkbox on death certificates

To ensure pregnancy-related deaths were being accurately captured in the U.S., the National Vital Statistics System in 2003 added a checkbox to death certificates to report whether the person who died was pregnant or had recently been pregnant. 

By 2014, when this study began, seven states still had not yet adopted the pregnancy checkbox. Therefore, to control for the checkbox, the study authors excluded those seven states (Alabama, Colorado, Georgia, Louisiana, Michigan, Ohio and West Virginia). 

"There's actually been a lot of controversy about whether or not the increase that's been observed is a true increase or is an artifact of how we're now collecting data," Khan said. "But when we examined deaths only in the states that had already adopted the checkbox and did it the exact same way, we captured an increase with acceleration in the last three years. While there are limitations with data capture from death certificates, they remain our best source for tracking this public health crisis." Study did not explore racial differences

The study authors used data from the Centers for Disease Control Wonder databases to examine all maternal deaths and live births from individuals aged 15 to 44 years old. 

One aspect of maternal death this study did not explore -; but is important to this discussion -; is the role that racial differences play. Black individuals are three times more likely to die from pregnancy-related deaths than white individuals. Khan said future studies will need to investigate this more in depth.  Source:

Northwestern UniversityJournal reference:

Hughes, Z. H., et al. (2024) Changes in Age Distribution and Maternal Mortality in a Subset of the US, 2014–2021. American Journal of Preventive Medicine. doi.org/10.1016/j.amepre.2024.02.011.