Background: Racial/ethnic minority women are known to have higher rates of preterm birth. Foreign-born immigrant women have lower rates of preterm births than US-born women despite more barriers to health care. Risk of stratified preterm birth, however, is not well-described; it is unknown how women’s race, ethnicity and nativity together affect risk of delivering extremely, moderately, or late preterm infants. Methods: We conducted a retrospective cohort study of women delivering a live birth in Pennsylvania from 2011-2014 using vital statistics linked to maternal records. Excluded from this study were infants with a gestational age < 23 weeks or > 44 weeks, birth weight < 400 grams or > 8000 grams, and infants with congenital anomalies. Preterm infants were stratified into 3 groups: late preterm (LPT, 34-36 6/7 weeks), moderately preterm (MPT, 29 to 33 6/7 weeks) vs. extremely preterm (EPT, < 29 weeks).Women were grouped into eight race/ethnicity/nativity categories: US non-Hispanic White (USNHW) and black (USNHB), US Hispanic White (USHW) and Black (USHB) vs. foreign-born (FB) for each racial/ethnic category. FBHB women were excluded due to the size of the cohort (<10 total). Bivariate and multivariate regression models determined the association between race, ethnicity, and nativity category and risk of each preterm birth strata. Results: Among the 515,074 dyads in our cohort, FBHW women had the lowest rates of prematurity overall (6.3%), compared to USNHB (12.5%) and FBNHB (8.9%). 80% of FBHW women’s preterm infants were LPT, compared to lower rates of LPT infants among FBNHB and USNHB women (63.1% and 64.6%, respectively). See figure 1 for the break-down of mothers by nativity/preterm stratification. USNHB and FBNHB women had the highest rates of EPT infants (14.06% and 11.42%, respectively). In adjusted models (figure 2), USNHB (aRR 2.1, 95% CI 1.9-2.3), USHB (aRR 2.2, 95% CI 1.1-4.1), and FBNHB (aRR 3.0, 95% CI 2.4-3.8) women had a higher risk of delivering an EPT infant when compared to USNHW women. Rates of EPT did not significantly differ for the other categories of women compared to USNHW women. When examining women who delivered MPT infants, USNHB women showed a higher risk as compared to USNHW (aRR 1.2, 95% CI 1.1-1.3). No other category of women showed a significantly higher risk of MPT compared to USNHW women. Conclusion: Foreign Born Hispanic white women’s risk of stratified preterm birth supports the immigrant paradox, but nativity and ethnicity do not appear to be protective for Black women with respect to risk of stratified preterm birth. A better understanding of how nativity mediates birth outcomes will help us understand the factors contributing to disparities within pregnant immigrant women and inform policies related their care.

Figure 1

Percent of mothers stratified by prematurity

Percentage fatty acid distribution of (A) eicosapentaenoic acid, (B) docosahexaenoic acid, and (C) arachidonic acid. (D) Total omega-6:omega-3 fatty acid ratio. Fish oil-based lipid emulsion (FOLE) in gray, and soybean oil-based lipid emulsion (SOLE) in black. P-values obtained from unpaired t-tests: (*) P<0.05, and (**) P<0.001.

Figure 1

Percent of mothers stratified by prematurity

Percentage fatty acid distribution of (A) eicosapentaenoic acid, (B) docosahexaenoic acid, and (C) arachidonic acid. (D) Total omega-6:omega-3 fatty acid ratio. Fish oil-based lipid emulsion (FOLE) in gray, and soybean oil-based lipid emulsion (SOLE) in black. P-values obtained from unpaired t-tests: (*) P<0.05, and (**) P<0.001.

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Figure 2

After adjusting for maternal age, insurance, education and medical comorbidities, Black women had higher risk of EPT, irrespective of ethnicity and nativity, compared to reference (US NHW). Foreign birth was a protective factor for all women in LPT category but was only protective for white women’s risk of a moderately preterm infant.

Figure 2

After adjusting for maternal age, insurance, education and medical comorbidities, Black women had higher risk of EPT, irrespective of ethnicity and nativity, compared to reference (US NHW). Foreign birth was a protective factor for all women in LPT category but was only protective for white women’s risk of a moderately preterm infant.

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