628 - Associations between Preterm Birth and Maternal Nativity and Residence in US Territories vs. Mainland US

Previous literature has shown that island-born Puerto Ricans tend to have higher rates of preterm birth (PTB) than mainland US-born women, which may indicate that being born in a US territory vs. a US state increases risk of PTB. Territory status for a region has been suggested to be a unique social determinant of health, yet there is limited research of its influence on perinatal outcomes like PTB, especially in territories other than Puerto Rico.

Objective:

To explore risk of PTB among birthing people who were born in and/or reside in US territories compared to those who were born in and/or reside in the mainland US.

Design/Methods:

This retrospective cohort study used restricted US National Vital Statistics data of singleton births from 2011 - 2018 (n = 22,470,753) in the US mainland and its territories (Puerto Rico, Guam, Virgin Islands, America Samoa, and Northern Marianas). Rates of PTB were compared by binary variables for maternal nativity (i.e., where a person is born) and maternal residence, as well as nativity and residence combined. PTB rates by nativity were also compared by specific territory of origin where available. Logistic regression models calculated the odds of PTB for birthing people born in or residing in each territory with US-mainland as the reference. Analyses were adjusted for maternal sociodemographic variables and medical comorbidities.

Results:

Overall, 8.1% of births to birthing people born on US mainland nativity were preterm compared to 10.6% of births to birthing people born in a territory. Individuals who were born on the mainland but resided in a territory and those with both territory nativity and residence had the highest unadjusted rates of PTB (10.8% and 11.4%, respectively, Fig. 1). Among birthing people born in US territories, rates of PTB were highest for those born in the Virgin Islands and lowest in American Samoa (Fig 2).  Individuals born in a US territory had 33% increased odds of PTB compared to those born in the US mainland; the odds increased to 50% when birthing people resided in a territory vs. the mainland (Table 1). Odds of PTB were highest for birthing people who were born in and/or resided in Puerto Rico.

Conclusion(s):

Being born in and/or residing in a US territory confers increased odds of preterm birth compared to being born in and/or residing in the mainland US. Environmental and contextual factors such as racism and colorism manifesting through differential policies impacting both healthcare access and social determinants of health may be contributing to these disparities.