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Prepregnancy Body Mass Index and Sudden Infant Death Syndrome

Wisborg, Kirsten; Vesterggard, Mogens; Kristensen, Janni; Kesmodel, Ulrik

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doi: 10.1097/01.ede.0000081992.98728.fb
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To the Editor:

Numerous risk factors for sudden infant death syndrome (SIDS) have been identified, including sleeping position, maternal smoking, maternal age below 20 years, and infant body temperature.1 In many countries, risk intervention campaigns have been followed by a notable decline in the incidence of SIDS during the last decade.2,3 However, many potentially preventable risk factors might yet remain unidentified. We have assessed a possible link between low prepregnancy body mass index (BMI) and SIDS.

We conducted a population-based cohort study of 24,399 liveborn singletons of Danish-speaking women booking for delivery at the Department of Obstetrics and Gynaecology, Aarhus University Hospital, Aarhus, Denmark, from September 1989-August 1996.4 This included approximately 90% of eligible infants. Information on prepregnancy weight, height, and maternal lifestyle factors was obtained from a questionnaire completed by the pregnant women at approximately 16 weeks of gestation. BMI was defined as the weight in kilograms divided by the square of the height in meters (kg/m2). Information about deaths during the first year of life was obtained from the Registry of Causes of Death, administered by the Danish National Board of Health, and from the Danish Civil Registration System, administered by the Danish Government. The International Classification of Diseases, 8th revision (ICD-8), was used in Denmark to classify causes of death through 1993, and from January 1994 the 10th revision (ICD-10) was used. SIDS was defined as death registered with ICD-8 code 795.80 and ICD-10 code R95.9. We reviewed the hospital records of all children from the cohort who died before 1 year of age to validate the cause of death.

As shown in the table, children of lean women had an almost 5-fold increased risk of SIDS (odds ratio = 4.9; 95% confidence interval = 1.7-14.2). The risk among children of overweight women was also increased. Adjusting for parity, maternal age, marital status, smoking, alcohol, and caffeine intake during pregnancy, years of schooling, employment status, and number of antenatal care visits did not substantially change the results. Conclusions were unchanged after restriction to nonsmokers and to women aged 20+ years (Table).

Association of Sudden Infant Death Syndrome (SIDS) With Prepregnancy Body Mass Index (BMI), Aarhus, Denmark, 1989–1996

Thus, our data suggest an increased risk of SIDS in women with a prepregnancy BMI of less than 20 kg/m2. Despite the small number of cases and control for a number of potential confounders, the confidence interval did not include 1.0. As a result of careful prospective collection of information about maternal lifestyle, sociodemographic and obstetric factors, we could adjust for a variety of potential confounders. Apparently, these factors did not explain the association between low BMI and SIDS. Unfortunately, we had no information about sleeping position, bottle feeding, and maternal weight gain during pregnancy. However, we consider it unlikely that differences in the distribution of these factors between women with a low and a normal BMI would explain our result.

Sullivan and Barlow1 have suggested that infants who die of SIDS are not completely normal in development, but possess some inherent weakness that compromises normal physiological defense mechanisms when subjected to stressful situations. The development of the respiratory or cardiovascular regulatory centers or of neuromuscular function might have been impaired in children of lean women as a result of a suboptimal intrauterine life. When these children are exposed to events such as sleeping prone, infections, or overheating, the response of the child might be inadequate and therefore fatal.

We suggest that low prepregnancy BMI might be associated with an increased risk of SIDS.

Kirsten Wisborg

Perinatal Epidmiological Research Unit

Department of Obstetrics and Gynecology

Aarhus University Hospital

8200 Aarhus, Denmark

Mogens Vesterggard

Janni Kristensen

Ulrik Kesmodel

University of Aarhus

Aarhus, Denmark


1.Sullivan FM, Barlow SM. Review of risk factors for sudden infant death syndrome. Paediatr Perinat Epidemiol. 2001;15:144–200.
2.Davidson RJ, Caldis S, Tonkin SL. New Zealand’s SIDS prevention program and reduction in infant mortality. Health Educ Q. 1995;22:162–171.
3.Wennergren G, Alm B, Oyen N, et al. The decline in the incidence of SIDS in Scandinavia and its relation to risk-intervention campaigns. Nordic Epidemiological SIDS Study. Acta Paediatr. 1997;86:963–968.
4.Wisborg K, Kesmodel U, Henriksen TB, et al. Exposure to tobacco smoke in utero and the risk of stillbirth and death in the first year of life. Am J Epidemiol. 2001;154:322–327.
5.Oyen N, Skjaerven R, Little RE, et al. Fetal growth retardation in sudden infant death syndrome (SIDS) babies and their siblings. Am J Epidemiol. 1995;142:84–90.
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