Maternal nativity and preterm birth disparities in twin pregnancies: A nationwide population-based study
Hiba J Mustafa1, Jana Karam2, William A Grobman3
1The Fetal Center at Riley Children's and Indiana University Health Division of Maternal-Fetal Medicine Indiana University School of Medicine Indianapolis Indiana USA.
Objective:
To evaluate whether maternal nativity (US born vs. non-US born) is associated with preterm birth (PTB) risk in individuals with twin pregnancies and to assess whether this association varies across racial and ethnic groups.
Methods:
This cross-sectional study used the National Center for Health Statistics and Centers for Disease Control and Prevention (CDC) natality dataset (2016-2023). This analysis included individuals aged 15-44 years with live-born twins residing in the United States. Maternal nativity (US born vs. non-US born) was stratified by race and ethnicity. Covariates included maternal age, education, insurance, prenatal care, smoking, prepregnancy body mass index, diabetes, hypertension, and year of birth. PTB (<37 weeks) was further categorized as extremely (<29 weeks), moderately (29-33weeks), and late (34-36 weeks). Binary and multinomial logistic regressions were used to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs).
Results:
Among 467,446 twin pregnancies, 282,754 (60.5%) were preterm. Of these, 191,972 (41.1%) were classified as late preterm (34 to <37 weeks), 68,457 (14.6%) as moderately preterm (29 to <34 weeks), and 22,325 (4.8%) as extremely preterm (<29 weeks). Non-US-born individuals had lower odds of PTB compared to US-born counterparts (aOR, 0.88; 95% CI, 0.86-0.89). The protective effect was strongest among non-US-born Black individuals (aOR, 0.65; 95% CI, 0.62-0.68). Across PTB subcategories, non-US-born individuals had reduced odds of extremely preterm (aOR, 0.85; 95% CI, 0.81-0.88), moderately preterm (aOR, 0.82; 95% CI, 0.80-0.84), and late PTB (aOR, 0.90; 95% CI, 0.88-0.92).
Conclusions:
Non-US-born individuals had lower odds of PTB compared to US-born individuals among twin pregnancies, extending prior findings from singleton populations to this high-risk group. These findings reinforce the role of nativity as an important social determinant of perinatal health. Future work should examine the mechanisms underlying these disparities and the influence of structural and cultural factors on twin birth outcomes.
