A case–control study of preterm delivery risk factors according to clinical subtypes and severity

Authors

  • Marisa Ip,

    1. Department of Epidemiology, Multidisciplinary International Research Training Program, University of Washington School of Public Health and Community Medicine,
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    • *

      These authors contributed equally to this work.

  • Elmera Peyman,

    1. Department of Epidemiology, Multidisciplinary International Research Training Program, University of Washington School of Public Health and Community Medicine,
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    • *

      These authors contributed equally to this work.

  • Vitool Lohsoonthorn,

    Corresponding author
    1. Department of Epidemiology, Multidisciplinary International Research Training Program, University of Washington School of Public Health and Community Medicine,
    2. Department of Preventive and Social Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
      Dr Vitool Lohsoonthorn, Department of Preventive and Social Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand. Email: vitool@gmail.com
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  • Michelle A. Williams

    1. Department of Epidemiology, Multidisciplinary International Research Training Program, University of Washington School of Public Health and Community Medicine,
    2. Center for Perinatal Studies, Swedish Medical Center, Seattle, Washington, USA; and
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  • Disclosure of Interest: No conflicts of interest.

Dr Vitool Lohsoonthorn, Department of Preventive and Social Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand. Email: vitool@gmail.com

Abstract

Aims:  To examine risk factors of preterm delivery (PTD) among Thai women.

Methods:  Our case–control study included 467 term controls and 467 PTD cases. PTD was studied in aggregate and in subgroups (i.e. spontaneous preterm labor and delivery [SPTD], preterm premature rupture of membrane [PPROM], medically indicated preterm delivery [MIPTD], moderate preterm delivery [32–36 weeks], and very preterm delivery [<32 weeks]). We used multivariable logistic regression procedures to estimate odds ratio (OR) and 95% confidence intervals (CI) of potential PTD risk factors.

Results:  Advanced maternal age (≥35 years) was associated with a 2.27-fold increased PTD risk overall (95%CI: 1.40, 3.68); and with a 3.79-fold increased risk of MIPTD (95%CI: 1.89, 7.59). Young maternal age (<20 years) was associated with a 2.07-fold increased risk of SPTD (95%CI: 1.19, 3.61). Prior history of PTD was associated with a 3.64-fold increased PTD risk overall (95%CI: 1.87, 7.09), and with a 5.69-fold increased risk of MIPTD (95%CI: 2.44, 13.24). No prenatal care was associated with all PTD subtypes. Lean women (body mass index < 18.5 kg/m2), compared with normal weight women (18.5–24.9 kg/m2), had a 1.70-fold increased risk of PTD (95%CI: 1.21, 2.39). Risk of SPTD (OR = 2.16, 95%CI: 1.44, 3.24) and very PTD (OR = 2.45, 95%CI: 1.35, 4.45) were also elevated in lean women.

Conclusions:  Maternal age, pre-pregnancy body mass index, prior history of PTD and no utilization of prenatal care were covariates identified in this study as risk factors for PTD. Our findings also suggest heterogeneity in risk factors for clinical subtypes of PTD.

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