# Maternal Nativity and Residence in US Territories and Preterm Birth

## TL;DR

Women born and living in US territories have a 30% higher risk of preterm birth compared to those on the mainland, with differences linked to insurance and prenatal care.

## Contribution

This study identifies a significant association between maternal territory status and increased preterm birth risk, modified by insurance type.

## Key findings

- Maternal territory nativity and residence are linked to a 30% higher preterm birth risk compared to mainland residents.
- Territory residents with Medicaid insurance had the highest preterm birth risk compared to mainland residents with private insurance.
- Insurance type and prenatal care access modify the association between territory status and preterm birth.

## Abstract

This cross-sectional study evaluates the association between maternal territory status and preterm birth, as well as whether insurance type modified associations.

What is the risk of preterm birth in US territories compared with the US mainland?

In this cross-sectional study of US birth certificate data from 28 627 700 births, individuals who were born and resided in US territories had a 30% increased risk of preterm birth compared with those who were born and resided on the mainland, an association that was modified by insurance status and prenatal care.

These findings suggest that maternal territory status is associated with increased risk of preterm birth; this may be due to contextual factors that differ between the US territories and the mainland, such as policies impacting prenatal care access.

US territory nativity and/or residence may be associated with health because it affects environmental exposures, insurance coverage, prenatal care, and other factors. Investigations of preterm birth in the US territories are limited.

To assess the association between maternal territory status and preterm birth, as well as whether insurance type modified associations.

Cross-sectional study of restricted-use birth certificates of in-hospital, singleton births in the US and territories from 2014 to 2023.

Maternal territory status was defined for births in territories where data were available (Guam, Northern Mariana Islands, Puerto Rico, and Virgin Islands) for the following groups: (1) those with territory nativity and residence; (2) those with territory nativity and mainland residence; (3) those with mainland nativity and territory residence; and (4) those with mainland nativity and residence (reference group). Insurance type (private, Medicaid, or other) was evaluated as well.

Preterm birth (live birth before 37 weeks’ gestation).

Among 28 627 700 births, 465 291 (1.6%) had any maternal territory status (nativity or residence). This group had a mean (SD) age of 27.1 (6.0) years, and 297 593 (64.0%) had Medicaid insurance. The highest preterm birth rate was among those with territory nativity and residence (10.5%; 95% CI, 10.4%-10.7%); the lowest was among those with mainland nativity and residence (8.4%; 95% CI, 8.4%-8.5%). Individuals with territory nativity and residence had an adjusted relative risk (aRR) of 1.30 (95% CI, 1.29-1.32) for preterm birth compared with the reference group. There was significant interaction between territory residence and insurance. Compared with individuals with mainland residence and private insurance, those with territory residence and Medicaid had the highest preterm birth risk (aRR, 1.57; 95% CI, 1.55-1.59), followed by territory residence and private insurance (aRR, 1.42; 95% CI, 1.39-1.45).

In this cross-sectional study, maternal territory nativity and residence were associated with preterm birth. Territory residence was associated with a higher risk of preterm birth, regardless of insurance type. Privately insured-individuals in US territories had a higher risk of preterm birth than Medicaid-insured individuals in the mainland. Given differential access to health care, health insurance, and other social exposures between territory and mainland populations, future work should explore causal effects and related policies that may improve birth outcomes in US territories.