<p><strong>OBJECTIVES: </strong>To explore the relative risks of preterm birth-both overall and stratified into three groups (late, moderate and extreme prematurity)-associated with maternal race, ethnicity and nativity (ie, birthplace) combined.</p>

<p><strong>STUDY DESIGN: </strong>This was a retrospective cross-sectional cohort study of women delivering a live birth in Pennsylvania from 2011-2014 (n=4,499,259). Log binomial and multinomial regression analyses determined the relative risks of each strata of preterm birth by racial/ethnic/native category, after adjusting for maternal sociodemographic, medical comorbidities and birth year.</p>

<p><strong>RESULTS: </strong>Foreign-born women overall had lower relative risks of both overall preterm birth and each strata of prematurity when examined en bloc. However, when considering maternal race, ethnicity and nativity together, the relative risk of preterm birth for women in different racial/ethnic/nativity groups varied by preterm strata and by race. Being foreign-born appeared protective for late prematurity. However, only foreign-born White women had lower adjusted relative risks of moderate and extreme preterm birth compared with reference groups. All ethnic/native sub-groups of Black women had a significantly increased risk of extreme preterm births compared with US born non-Hispanic White women.</p>

<p><strong>CONCLUSIONS: </strong>Race, ethnicity and nativity contribute differently to varying levels of prematurity. Future research involving birth outcome disparities may benefit by taking a more granular approach to the outcome of preterm birth and considering how nativity interacts with race and ethnicity.</p>