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Women's prepregnancy underweight as a risk factor for preterm birth: a retrospective study.

CPQCC Publication
TitleWomen's prepregnancy underweight as a risk factor for preterm birth: a retrospective study.
Publication TypeJournal Article
Year of Publication2016
AuthorsGirsen AI, Mayo JA, Carmichael SL, Phibbs CS, Shachar BZ, Stevenson DK, Lyell DJ, Shaw GM, Gould JB
Corporate AuthorsMarch of Dimes Prematurity Research Center at Stanford University School of Medicine
Date Published2016 Nov
KeywordsAdult, Body Mass Index, California, Female, Gestational Age, Humans, Infant, Newborn, Parity, Pregnancy, Premature Birth, Retrospective Studies, Risk Factors, Severity of Illness Index, Thinness

OBJECTIVE: To investigate the distribution of known factors for preterm birth (PTB) by severity of maternal underweight; to investigate the risk-adjusted relation between severity of underweight and PTB, and to assess whether the relation differed by gestational age.

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 analysed. Singleton live births of women whose prepregnancy body mass index (BMI) was underweight (<18.5 kg/m ) or normal (18.50-24.99 kg/m ) were analysed. Underweight BMI was further categorised as: severe (<16.00), moderate (16.00-16.99) or mild (17.00-18.49). PTB was grouped as 22-27, 28-31, 32-36 or <37 weeks (compared with 37-41 weeks). Adjusted multivariable Poisson regression modeling was used to estimate relative risk for PTB.


RESULTS: About 72 686 (7.6%) women were underweight. Increasing severity of underweight was associated with increasing percent PTB: 7.8% (n = 4421) in mild, 9.0% (n = 1001) in moderate and 10.2% (475) in severe underweight. The adjusted relative risk of PTB also significantly increased: adjusted relative risk (aRR) = 1.22 (95% CI 1.19-1.26) in mild, aRR = 1.41 (95% CI 1.32-1.50) in moderate and aRR = 1.61 (95% CI 1.47-1.76) in severe underweight. These findings were similar in spontaneous PTB, medically indicated PTB, and the gestational age groupings.

CONCLUSION: Increasing severity of maternal prepregnancy underweight BMI was associated with increasing risk-adjusted PTB at <37 weeks. This increasing risk was of similar magnitude in spontaneous and medically indicated births and in preterm delivery at 28-31 and at 32-36 weeks of gestation.

TWEETABLE ABSTRACT: Increasing severity of maternal underweight BMI was associated with increasing risk of preterm birth.

Alternate JournalBJOG
PubMed ID27172996
PubMed Central IDPMC5069076
Grant ListUL1 TR001085 / TR / NCATS NIH HHS / United States