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Preterm Birth and Gestational Length in Four Race–Nativity Groups, Including Somali Americans

Oliver, Emily, A., MD, MPH; Klebanoff, Mark, MD; Yossef-Salameh, Lina, MD; Oza-Frank, Reena, PhD; Moosavinasab, Soheil, MS; Reagan, Patricia, PhD; Muglia, Louis, MD, PhD; Buhimschi, Catalin, S., MD; MBA; Buhimschi, Irina, A., MD

doi: 10.1097/AOG.0000000000002427
Contents: Original Research

OBJECTIVE: To compare preterm birth rates and gestational length in four race–nativity groups including Somali Americans.

METHODS: Using a retrospective cohort study design of Ohio birth certificates, we analyzed all singleton births between 2000 and 2015 from four groups of women categorized as U.S.-born, non-Hispanic white (USBW), U.S.-born, non-Hispanic black (USBB), African-born black (ABB, primarily of West African birth country), and Somalia-born (SB). An algorithm trained on maternal names was used to confirm Somali ethnicity. Gestational length was analyzed as completed weeks or aggregated by clinically relevant periods. Risk of spontaneous and health care provider–initiated preterm birth was calculated in a competing risk model.

RESULTS: Births to women in the designated groups accounted for 1,960,693 births (USBW n=1,638,219; USBB n=303,028; ABB n=10,966, and SB n=8,480). Women in the SB group had a lower preterm birth rate (5.9%) compared with women in the USBB (13.0%), ABB (8.4%), and USBW (7.9%) groups (P<.001). Women in the SB group had a higher frequency of postterm pregnancy (5.8% vs less than 1%, P<.001 for all groups). The lower rate of preterm birth in the SB group was unrelated to differences in parity or smoking or whether preterm birth was spontaneous or health care provider–initiated. The lower rate of preterm birth and tendency for prolonged gestation was attenuated in ethnic Somali women born outside Somalia.

CONCLUSION: We report a positive disparity in preterm birth and a tendency for prolonged gestation for ethnic Somali women in Ohio. Etiologic studies in multiethnic cohorts aimed to uncover the sociobiological determinants of gestational length may lead to practical approaches to reduce prematurity in the general population.

Compared with other race–nativity groups, Somali women in Ohio have lower preterm birth rates and a higher rate of postterm pregnancies.

Center for Perinatal Research, the Research Institute at Nationwide Children's Hospital, the Departments of Obstetrics and Gynecology and Pediatrics and the College of Public Health, The Ohio State University, and Research Information Solutions and Innovation (RISI), the Research Institute at Nationwide Children's Hospital, Columbus, and Cincinnati Children's Hospital Medical Center, Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati, Ohio.

Corresponding author: Irina A. Buhimschi, MD, Center for Perinatal Research, The Research Institute at Nationwide Children's Hospital, Columbus, OH 43215; email:

Supported by the March of Dimes through the March of Dimes Prematurity Research Center Ohio Collaborative.

Financial Disclosure The authors did not report any potential conflicts of interest.

Presented in part at the 35th Annual Meeting of the Society for Maternal-Fetal Medicine, February 2–7, 2015, San Diego, California.

The authors thank medical and research staff at The Ohio State University and Mount Carmel System for their support and assistance. The funding source had no role in study design, data analysis, writing of the report, or decision to submit for publication. This study includes data provided by the Ohio Department of Health, which should not be considered an endorsement of this study or its conclusions.

Each author has indicated that he or she has met the journal's requirements for authorship.

© 2018 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.