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BJOG. Author manuscript; available in PMC 2017 November 01. Published in final edited form as: BJOG. 2016 November ; 123(12): 2001–2007. doi:10.1111/1471-0528.14027.

Women’s prepregnancy underweight as a risk factor for preterm birth: a retrospective study Anna I Girsen1, Jonathan A Mayo2, Suzan L Carmichael2, Ciaran S Phibbs2,3, Bat Zion Shachar2, David K Stevenson2, Deirdre J Lyell1, Gary M Shaw2, and Jeffrey B Gould2 on behalf of On behalf of the March of Dimes Prematurity Research Center at Stanford University School of Medicine

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1Department

of Obstetrics & Gynecology, Stanford University School of Medicine, Stanford, CA

2Department

of Pediatrics, Division of Neonatal and Developmental Medicine, Stanford University School of Medicine, Stanford, CA 3Health

Economics Resource Center, Veterans Affairs Palo Alto Healthcare System, Menlo Park,

CA

Abstract Objective—To investigate the distribution of known factors for preterm birth (PTB) by severity of maternal underweight; to investigate the risk adjusted relationship between severity of underweight and PTB and to assess if the relationship differed by gestational age.

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Design—Retrospective cohort study. Setting—State of California, USA. Methods—Maternally linked hospital and birth certificate records of 950,356 California deliveries in 2007–2010 were analyzed. Singleton live births of women whose pre-pregnancy body mass index (BMI) was underweight (