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Maternal overweight and obesity in early pregnancy and risk of infant mortality: a population based cohort study in Sweden

BMJ 2014; 349 doi: (Published 02 December 2014) Cite this as: BMJ 2014;349:g6572
  1. Stefan Johansson, consultant neonatologist1,
  2. Eduardo Villamor, associate professor of epidemiology2,
  3. Maria Altman, postdoctoral researcher1,
  4. Anna-Karin Edstedt Bonamy, paediatrician1,
  5. Fredrik Granath, associate professor of medical statistics1,
  6. Sven Cnattingius, professor of reproductive epidemiology1
  1. 1Clinical Epidemiology Unit, Department of Medicine, Solna, Karolinska University Hospital, Karolinska Institutet, SE-171 76 Stockholm, Sweden
  2. 2Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, Michigan, United States
  1. Correspondence to: S Johansson stefan.johansson{at}
  • Accepted 15 October 2014


Objective To investigate associations between maternal overweight and obesity and infant mortality outcomes, including cause-specific mortality.

Design Population based cohort study.

Setting and participants 1 857 822 live single births in Sweden 1992–2010.

Main outcome measures Associations between maternal body mass index (BMI) in early pregnancy and risks of infant, neonatal, and postneonatal mortality, overall and stratified by gestational length and by causes of infant death. Odds ratios were adjusted for maternal age, parity, smoking, education, height, country of birth, and year of delivery.

Results Infant mortality rates increased from 2.4/1000 among normal weight women (BMI 18.5–24.9) to 5.8/1000 among women with obesity grade 3 (BMI ≥40.0). Compared with normal weight, overweight (BMI 25.0–29.9) and obesity grade 1 (BMI 30.0–34.9) were associated with modestly increased risks of infant mortality (adjusted odds ratios 1.25 (95% confidence interval 1.16 to 1.35) and 1.37 (1.22 to 1.53), respectively), and obesity grade 2 (BMI 35.0–39.9) and grade 3 were associated with more than doubled risks (adjusted odds ratios 2.11 (1.79 to 2.49) and 2.44 (1.88 to 3.17)). In analyses stratified by preterm and term births, maternal BMI was related to risks of infant mortality primarily in term births (≥37 weeks), where risks of deaths due to birth asphyxia and other neonatal morbidities increased with maternal overweight and obesity. Obesity grade 2–3 was also associated with increased infant mortality due to congenital anomalies and sudden infant death syndrome.

Conclusions Maternal overweight and obesity are associated with increased risks of infant mortality due to increased mortality risk in term births and an increased prevalence of preterm births. Maternal overweight and obesity may be an important preventable risk factor for infant mortality in many countries.


  • Contributors: SJ, EV, FG, and SC conceived and designed the study. SC acquired data. SJ, EV, MA, AEB, FG, and SC analysed and interpreted the data, and wrote and critically revised the manuscript. SJ, FG, and SC performed the statistical analysis and provided administrative, technical, and material support. SC obtained funding and supervised the study.

  • Funding: An unrestricted grant from Karolinska Institutet (Distinguished Professor Award to SC) and from the Swedish Research Council for Health, Working Life and Welfare (project No 2014–0073).

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.”

  • Ethical approval: The study was approved by the Research Ethics Committee at Karolinska Institutet, Stockholm, Sweden (No 2012/4:9).

  • Data access: All authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analyses.

  • Transparency: The manuscript is an honest, accurate, and transparent account of the study being reported. No important aspects of the study have been omitted. There are no discrepancies from the study as planned.

  • Data sharing: No additional data available.

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