Researchers from Boston Medical Center, in collaboration with colleagues at the University of Massachusetts Chan Medical School and the Harvard T.H. Chan School of Public Health, have identified a troubling trend in preterm birth rates in the United States. Between 2011 and 2021, these rates increased significantly among households earning less than 200% of the federal poverty level, while remaining stable for higher-income households. Notably, Black mothers experienced the highest rates of preterm births across all income categories.
Preterm birth, defined as delivery before 37 weeks of gestation, is a leading cause of infant mortality and morbidity in the United States. Previous studies have established that Black individuals face approximately twice the risk of preterm birth compared to their white counterparts—a disparity that has persisted for decades. The intersection of household income with race and ethnicity plays a critical role in this issue, affecting access to nutritious food, quality healthcare, and exposure to environmental pollutants, as well as contributing to chronic health conditions and stress.
Examining Trends Over a Decade
The study titled “Trends in US Preterm Birth Rates by Household Income and Race and Ethnicity,” published in JAMA Network Open, utilized nationally representative data to analyze preterm birth trends from 2011 to 2021. The researchers examined data from 411,469 mothers and their infants, categorizing race and ethnicity into six groups: American Indian or Alaska Native, Asian, Hispanic, non-Hispanic Black, non-Hispanic white, and other races or multiracial.
Data were collected through the Pregnancy Risk Assessment Monitoring System (PRAMS), a perinatal surveillance system developed by the Centers for Disease Control and Prevention (CDC), with state health departments administering the surveys. Mothers answered questions two to four months postpartum, providing demographic information, pregnancy characteristics, and infant outcomes. The study conservatively estimated income status by assuming the upper value of each income band and relating it to the federal poverty level based on year, state, and household size.
For reference, the 2025 guideline for 100% of the federal poverty level was set at $15,650 for a one-person household and $26,650 for a three-person household.
Income and Racial Disparities in Preterm Birth Rates
The research revealed concerning averages for preterm birth rates: 10.4% for households earning less than 100% of the federal poverty level, 8.9% for those at 100% to 199%, and 7.5% for households at 200% or more. Rates increased among households below 100% from 9.7% in 2011 to 11.1% in 2021, and for households earning between 100% and 199%, from 7.8% to 10.0%. In contrast, the rate for households at 200% or more remained relatively stable at around 8.0% in 2011 and 8.1% in 2021.
Among different racial and ethnic groups, the highest preterm birth rates consistently occurred in households earning below 100% of the poverty level, with the exception of Asian individuals. Black mothers exhibited the highest preterm birth rates across all income levels. The adjusted risk analysis revealed that Black mothers at the lowest income level faced a 19% higher relative risk of preterm birth compared to white mothers, while at the highest income level, their risk remained 13% higher.
The close alignment of race and ethnicity with income in the dataset indicated that when both factors were analyzed together, race effectively captured the disparities previously attributed to income alone. Alarmingly, Black mothers in the highest income bracket experienced higher preterm birth rates than white mothers in the lowest income group.
The researchers concluded that disparities in preterm birth based on household income have widened over time. They emphasized the need to investigate the impact of systemic racism and racial inequality on these outcomes. Public health initiatives aimed solely at addressing income disparities may not be sufficient. Efforts should also tackle the socioeconomic and structural inequities that disproportionately affect Black communities.
Proposed interventions could focus on improving access to timely and comprehensive prenatal care, addressing chronic health conditions among mothers, reducing stressors, and mitigating racial and ethnic discrimination in healthcare settings.
As the study highlights, understanding the complex relationship between race, income, and health outcomes is crucial for developing effective strategies to reduce inequities in preterm birth rates.
