Cause-specific infant mortality in a population-based Swedish study of term and post-term births: the contribution of gestational age and birth weight
- 1Department of Medicine Solna, Clinical Epidemiological Unit, T2 Karolinska Institutet, Stockholm, Sweden
- 2Department of Clinical Science, Technology and Intervention, Pediatric Unit, Karolinska Institutet, Stockholm, Sweden
- 3Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden
- Correspondence to Dr Maria Altman;
- Received 13 March 2012
- Accepted 31 May 2012
- Published 4 July 2012
Objective To investigate infant mortality and causes of infant death in relation to gestational age (GA) and birth weight for GA in non-malformed term and post-term infants.
Design Observational, retrospective nationwide cohort study.
Setting Sweden 1983–2006.
Participants 2 152 738 singleton non-malformed infants born at 37 gestational weeks or later.
Main outcome measures Infant, neonatal and postneonatal mortality and causes of infant death.
Results Infant mortality rate was 0.12% (n=2687). Compared with infants born at 40 weeks, risk of infant mortality was increased among early term infants (37 weeks, adjusted OR 1.70, 95% CI 1.43 to 2.02). Compared with infants with normal birth weight for GA, very small for gestational age (SGA; <3rd percentile) infants faced a doubled risk of infant mortality (adjusted OR 2.13, 95% CI 1.80 to 2.53), and corresponding risk was also increased among moderately SGA infants (3rd to <10th percentile; adjusted OR 1.46, 95% CI 1.26 to 1.68). Sudden infant death syndrome (SIDS) was the most common cause of death, accounting for 39% of all infant mortality. Compared with birth at 40 weeks, birth at 37 weeks was associated with increased risks of death by infections, cardiovascular disorders, SIDS and malignant neoplasms. Very and moderately SGA were associated with increased risks of death by neonatal respiratory disorders, infections, cardiovascular disorders, SIDS and neuromuscular disorders. High birth weight for GA was associated with increased risks of death by asphyxia and malignant neoplasms.
Conclusion Early term birth and very to moderately low birth weight for GA are independent risk factors for infant mortality among non-malformed term infants.
To cite: Altman M, Edstedt Bonamy A-K, Wikström A-K, et al. Cause-specific infant mortality in a population-based Swedish study of term and post-term births: the contribution of gestational age and birth weight. BMJ Open 2012;2:e001152. doi:10.1136/bmjopen-2012-001152
Contributors All authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis, and the study hypothesis arose before inspection of the data. MA has contributed to the design and conduct of the study; collection, management, analysis and interpretation of the data; and preparation of the manuscript. A-KEB has contributed to the design and conduct of the study, interpretation of the data and review of the manuscript. A-KW has contributed to the design and conduct of the study, interpretation of the data and review of the manuscript. SC has contributed to the design and conduct of the study; collection, management and interpretation of the data; and review of the manuscript. The final version of the manuscript has been approved by all authors.
Funding This work was supported by the European Union's Seventh Framework Programme (FP7/2007-2011).
Competing interests None.
Ethics approval Ethics approval was provided by the Ethics Committee at Karolinska Institutet, Stockholm.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The statistical code is available from the corresponding author (firstname.lastname@example.org). Participants consent was not obtained but the presented data are anonymised and risk of identification is low.
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