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. 2014 Dec 2:349:g6572.
doi: 10.1136/bmj.g6572.

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

Stefan Johansson  1 , Eduardo Villamor  2 , Maria Altman  3 , Anna-Karin Edstedt Bonamy  3 , Fredrik Granath  3 , Sven Cnattingius  3
Affiliations

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

Stefan Johansson et al. BMJ. .

Abstract

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.

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Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf 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.”

Figures

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Fig 1 Births in Sweden 1992–2010. The study population includes 1 857 822 live single births in Sweden 1992–2010. Numbers of births with missing information on maternal body mass index (BMI), smoking status, education level, and country of birth are provided
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Fig 2 Formula for calculating population attributable fraction (PAF)
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Fig 3 Maternal body mass index (BMI) in early pregnancy and risks of infant, neonatal, and postneonatal mortality (deaths during first year, deaths within 28 days of life, and deaths after 28 days to 1 year, respectively). Odds ratios were estimated both from the dataset with complete covariate information (n= 1 545 635 for infant and neonatal mortality and n= 1 543 054 for postneonatal mortality) and after multiple imputation of missing values (n= 1 857 822 for infant and neonatal mortality and n= 1 854 356 for postneonatal mortality). Odds ratios were adjusted for maternal age, parity, smoking, education, height, country of birth, and year of delivery
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