About one in every 10 U.S. births occurs before 37 weeks gestation. Infants born this early are considered preterm, and they face an increased risk of mortality and lifelong impairments compared with term infants.

Race and ethnicity have been strongly linked to preterm birth rates. For example, in 2020, Black birthing people experienced 50% higher rates of preterm birth than their non-Hispanic White counterparts.

Less is known about the role of maternal nativity—which refers to a person’s country of origin—on preterm births. In a new study, LDI Senior Fellow Dr. Diana Montoya-Williams and her team explore how risks of preterm birth vary across maternal ethnicity, race, and nativity.

Understanding Nativity in Relation to Preterm Birth

Individuals who were born outside of the United States but now live in this country have better health outcomes than U.S.-born members of the same racial or ethnic group, according to the phenomenon of the “Immigrant Paradox.” However, this paradox is not reflected across all racial and ethnic groups. “Belonging to certain racial and ethnic categories shape key parts of our lived and constructed experiences,” says Montoya-Williams. “The Immigrant Paradox doesn’t apply universally, so we need to consider the nuances of race and ethnicity when studying preterm birth.”

Different aspects of a birthing person’s identity may result in various structural or individual-level advantages or disadvantages. Nativity can serve as a proxy for citizenship, preferred language, or exposure to discrimination, providing deeper insight into the factors that influence birthing outcomes across and within racial or ethnic groups. For example, despite being born outside of the United States, Black immigrants may face structural and interpersonal racism when seeking health care. This racism can increase their risk of experiencing adverse birth outcomes, such as preterm birth.

Inconsistencies in Preterm Birth Rates Across Race, Ethnicity, and Nativity

The researchers analyzed over 34 million live births between 2009 and 2018 using information from birth certificates on maternal race and ethnicity, self-reported country of birth, and preterm birth.

Across all nativity, ethnicity, and race subgroups, most had an increased risk of preterm birth compared to U.S.-born White birthing people.

Only two groups fared better: Non-U.S.-born Hispanic individuals and non-U.S.-born White individuals.

However, comparisons to immigrants within groups showed more nuanced results. Non-U.S.-born birthing people who were Asian, Hispanic, Black or White experienced a lower risk of preterm birth compared to their U.S.-born counterparts. In contrast, risk of preterm birth was higher for non-U.S.-born Native Hawaiian/Other Pacific Islander and American Indian or Alaska Native birthing people compared to their U.S-born counterparts.

Ultimately, the researchers obtained a more detailed understanding of how racial and ethnic disparities in preterm birth persist in the United States when they considered the intersectional aspects of a birthing person’s identity. Furthermore, failing to take nativity and other important factors into account obscured disparities and may impede pathways to intervention.

Implications for Policy and Practice

The study’s findings highlight the importance of investigating nativity, along with race and ethnicity, to paint a more complete picture of preterm birth risk. For example, the study uncovered differences in birth outcomes among two understudied populations: American Indian or Alaska Native and Native Hawaiian or Other Pacific Islander. Given their small proportion within the U.S. population, these communities are often incorporated into the broader “Asian” racial subgroup. This oversimplification may obscure other differences in health outcomes within each population, resulting in underrepresentation in health research and policy.

Strategies are needed to ensure that birthing people from underrepresented communities benefit from research and health care interventions. For example, innovative ways to account for individuals who select the “Other” racial and ethnic category should be explored. Two ways to make datasets more inclusive are to (1) offer detailed self-identification options on surveys and (2) utilize machine-learning techniques to better evaluate responses in the “Other” category. 

Additionally, methodological and statistical methods need to be improved to better support how race and ethnicity are categorized in research. This March, the Office of Management and Budget updated standards for maintaining, collecting and presenting race and ethnicity data across federal agencies. The most notable changes include the addition of a Middle Eastern and North African category, and the combination of race and ethnicity.

“As the ways we categorize race and ethnicity change, so will epidemiological patterns,” said Montoya-Williams, “Studying these changes will allow us to better understand and address disparities in preterm birth.”

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The study, “Preterm Birth Risk and Maternal Nativity, Ethnicity, and Race” was published on March 21, 2024, in JAMA Network Open. Authors include Alejandra Barreto, Brielle Formanowski, Michelle-Marie Peña, Elizabeth G. Salazar, Sara C. Handley, Heather H. Burris, Robin Ortiz, Scott A. Lorch, and Diana Montoya-Williams.

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