Infant mortality rate rises sharply when mothers experience pregnancy-associated death

A new study found that infant mortality rates in Massachusetts were 14 times higher among babies whose mother experienced a pregnancy-associated death than among babies whose mother survived pregnancy and postpartum.

​​Global health research has long shown the devastating consequences that maternal deaths have on families and communities in developing countries where maternal mortality rates are high. But this insight is rare in the United States, despite the nation maintaining the highest rate of maternal mortality among its peer nations.

A new study led by a Boston University School of Public Health (BUSPH) researcher captures the first data in decades on the relationship between maternal deaths and infant health and deaths, finding that infants are much more likely to die or be hospitalized for poor health if their mother experiences a pregnancy-associated death or severe illness. 

Published in the journal Obstetrics & Gynecology, the study examined maternal and infant health and mortality rates in Massachusetts from 1999 to 2021 and found that in cases when the mother died during pregnancy or the postpartum period, the infant mortality rate was more than 14 times as high as in cases when the mother did not die during this period. When maternal deaths occurred after mothers experienced severe maternal morbidity (SMM), the infant mortality rate was 22 times greater than when the mother survived the postpartum period.

Furthermore, nonpremature infants who survived after their mother's pregnancy-associated death were still 35 percent more likely to be hospitalized within their first year of life, and 10 percent more likely to be hospitalized if their mother experienced a health condition associated with SMM. 

These findings help quantify the intrinsic relationship between a mother's health and their infant's health. As states' maternal mortality review committees are being reduced or eliminated entirely, the researchers hope the results underscore the need to increase, rather than decrease, support for women's health-for the benefit of mothers' health, as well as the health of their children, families, and communities.

If we want to protect infant health, the first step is to recognize the shared health outcomes between mothers and their infants. Improving women's health is a worthy goal in itself, but this research reminds us that healthier mothers are also the foundation for protecting the health of their infants and, ultimately, their families."

Dr. Eugene Declercq, study lead author, professor of community health sciences at BUSPH

For the study, Dr. Declercq and colleagues at BUSPH, Tufts University School of Medicine, the Massachusetts Department of Public Health, the University of Colorado, and Evalogic Services, Inc. utilized statewide data on Massachusetts hospital records regarding maternal and infant health and deaths from 1999 to 2021. Among 1,617,054 live births between 1999 and 2020, there were 474 pregnancy-associated maternal deaths, defined as deaths from any cause during pregnancy or up to one year postpartum.

The overall pregnancy-associated death ratio in Massachusetts was 29.3 per 100,000 live births and the overall infant mortality rate was 4.06 per 1,000 live births. When mothers died, the infant mortality rate was 55 per 1,000 deaths, and that rate increased to 87.9 per 1,000 deaths when the mother had a condition associated with SMM, such as renal failure, high blood pressure, eclampsia, and sepsis.

Consistent with prior research, the study identified the relationship of infant deaths to other potential risk factors, including births to mothers who were older than 40, as well as mothers who had public insurance, used opioids, had a poor health history, had more than one baby at a time, or were non-Hispanic Black-but the links between infant death and SMM or pregnancy-associated death were much stronger than any other risk factor.

Mothers' deaths during the study period were most strongly associated with SMM, a history of opioid use, and having four or more children. Some of the causes of infant mortality were hypoxic ischemic encephalopathy and congenital heart defects among premature babies, while full-gestation infants experienced deaths from injuries, birth asphyxia, congenital malformation, and unknown causes.

Notably, Massachusetts had the lowest infant mortality rate in the country during the study period, so while these results may not be nationally representative, it's likely that other states are facing more dire infant health consequences as a result of maternal morbidity and mortality.

"Our extensive work using longitudinally linked data in the Pregnancy-to-Early Life database in Massachusetts has importantly shown that there are missed opportunities to identify and follow mothers and their children for adverse health outcomes," says study coauthor Dr. Howard Cabral, professor of biostatistics at BUSPH. "Investing in maternal health is critical for public health policy and practice."