Research conducted by teams at Boston Medical Center, the University of Massachusetts Chan Medical School, and the Harvard T.H. Chan School of Public Health reveals a troubling increase in preterm birth rates in the United States between 2011 and 2021. The study indicates that households earning less than 200% of the federal poverty level experienced rising rates of preterm births, while rates remained stable among higher-income households. Notably, Black mothers exhibited the highest preterm birth rates across all income levels.
The implications of these findings are significant, as preterm birth, defined as delivery before 37 weeks of gestation, continues to be the leading cause of infant mortality and morbidity in the United States. Previous research has established that Black individuals face approximately twice the risk of preterm birth compared to their white counterparts, a disparity that has persisted for decades.
Economic factors intersect with race and ethnicity, influencing preterm birth risks through various mechanisms. These include neighborhood environments, access to nutritious food, the quality of health care, exposure to environmental pollutants, and the impacts of chronic conditions and stress.
The study, titled “Trends in US Preterm Birth Rates by Household Income and Race and Ethnicity,” was published in JAMA Network Open. It utilized nationally representative data to analyze trends in preterm births across different income brackets from 2011 to 2021, focusing on a sample of 411,469 mothers and their infants. The racial and ethnic categories included American Indian or Alaska Native, Asian, Hispanic, non-Hispanic Black, non-Hispanic white, and other races or multiracial individuals.
The researchers leveraged the Pregnancy Risk Assessment Monitoring System (PRAMS), a perinatal surveillance system developed by the Centers for Disease Control and Prevention (CDC) and administered by state health departments. Mothers completed surveys two to four months postpartum, with responses linked to birth certificate data to provide demographic information, pregnancy characteristics, and infant outcomes.
Annual household income was reported in categorical ranges, and the researchers conservatively estimated income status by assuming the upper value of each income band. For context, the guideline for 100% of the federal poverty level was $15,650 for a one-person household and $26,650 for a three-person household in 2025.
The findings revealed that preterm birth rates averaged 10.4% for households earning less than 100% of the federal poverty level, 8.9% for those earning between 100% and 199%, and 7.5% for households with incomes at 200% or more. The rates in households earning less than 100% increased from 9.7% in 2011 to 11.1% in 2021, while those earning between 100% and 199% saw a rise from 7.8% to 10.0%. In contrast, the rates for households earning 200% or more remained relatively stable, at 8.0% in 2011 and 8.1% in 2021.
Within most racial and ethnic groups, the highest preterm birth rates were seen in households earning less than 100%, with Asian individuals being the only exception. Black mothers consistently displayed the highest preterm birth rates, regardless of income level. The analysis indicated that Black mothers at the lowest income level faced a 19% higher adjusted relative risk of preterm birth compared to white mothers, while the risk was 13% higher for those in the highest income group. Differences among middle-income groups were not statistically significant.
The research concluded that disparities in preterm birth rates linked to household income have widened over the past decade. The associations between race and income highlight the need to examine the impacts of systemic racism and inequality on preterm birth rates. The study suggests that public health initiatives aimed at reducing preterm birth may be ineffective if they focus solely on income.
To address these issues, the researchers advocate for policies that tackle socioeconomic factors and structural inequities disproportionately impacting Black communities. Proposed interventions could enhance access to timely and comprehensive prenatal care, address maternal chronic health conditions, alleviate stress, and mitigate racial and ethnic discrimination in health care settings.
As the data underscores the intersectionality of race, income, and health outcomes, further exploration into these relationships is essential for developing effective public health strategies aimed at improving maternal and infant health outcomes in the United States.
