Severe maternal morbidity (SMM), which refers to unexpected labor and delivery outcomes that can cause life-threatening maternal health problems, is on the rise in the United States and has been estimated to impact between 50,000 to 60,000 birthing people each year, according to the latest data compiled in 2014 by the Centers for Disease Control and Prevention.

However, these estimates have been based on cases identified during hospitalization for delivery, and do not reflect maternal health complications that may occur during pregnancy or the postpartum period.

A new study led by a School of Public Health researcher has found that excluding prenatal and postpartum health complications in SMM measurements substantially underestimates the burden of maternal morbidity in the US.

Published in the journal Obstetrics & Gynecology, the study examined cases of SMM during prenatal, delivery, and postpartum hospitalizations from 2009 to 2018 in Massachusetts and identified an additional 22 percent of cases that met SMM criteria. If the 2018 rates of SMM in Massachusetts with this expanded measurement were applied nationally, the true number of cases could be closer to 90,000 per year.

Using a longitudinally linked database, the study is the first of its kind to examine SMM during pregnancy, at birth, and postpartum.

“For this project, we expanded the focus of SMM from birth to women’s health through the entire perinatal period,” says study lead author Eugene Declercq, professor of community health sciences. “The data overwhelmingly show that it is time to develop measures that more sensitively identified severe morbidities during pregnancy and postpartum.”

Declercq and colleagues analyzed data from the Pregnancy to Early Life Longitudinal (PELL) database, a Massachusetts data system that links records from birth certificates, delivery hospital discharge records, and non-birth hospital records for all birthing people. Using CDC algorithms that define SMM criteria, the researchers examined nearly 600,000 deliveries, as well as hospitalizations during pregnancy and through 42 days postpartum, from January 2009 to December 2018. SMM increased steadily over the study period, from 129.4 cases per 10,000 deliveries in 2009 to 214.3 cases per 10,000 deliveries in 2018.

Aside from blood transfusions, which cause the largest percentage of SMM cases, the leading causes for additional cases of severe morbidity during pregnancy and postpartum were sepsis, thrombotic embolism, and adult respiratory distress syndrome.

“Our findings underscore the need for a greater investment in outpatient, community-based programs and quality improvement initiatives,” Declercq says, citing examples such as standardized, outpatient risk assessment screening for venous thromboembolism, prevention of maternal peripartum infections via screening and vaccinations, and postpartum home blood pressure monitoring for birthing individuals at increased risk.

The study is the first of several publications by the research team, as part of a larger project on SMM that is funded by the National Institutes of Health. The next two studies, informed by this first publication, will examine differences in SMM by race/ethnicity and an intervention at five hospitals in Massachusetts to assess the impact of doula care on pregnancy outcomes among Black women.