Do differences in the prevalence of risk factors explain the higher mortality from sudden infant death syndrome in New Zealand compared with the UK?

AIMS

To compare the prevalence of risk factors for the sudden infant death syndrome (SIDS) in New Zealand (SIDS mortality 3.53/1000) with that in the South West Thames (SWT) region of the United Kingdom (SIDS mortality 1.36/1000).

METHODS

The methodology of the study was essentially identical in New Zealand and SWT. The subjects in both countries were randomly selected from all births in the study regions. The subjects were randomly allocated an age at which to be interviewed using the same questionnaire in the two study areas. Obstetric records were also examined. Eighteen hundred subjects were selected in New Zealand and 700 subjects in SWT.

RESULTS

Younger and unmarried mothers were slightly more common in New Zealand than in SWT. The prevalence of maternal smoking, prone sleeping position and infants' sharing of beds with another person were all higher in New Zealand than SWT, thus increasing the risk of SIDS (maternal smoking in pregnancy: 31.0% vs 23.8% respectively, chi 2 = 11.6, p = 0.001; prone sleeping position: 32.9% vs 25.9%, chi 2 = 18.9, p < 0.001; bed sharing: 10.5% vs 6.8%, chi 2 = 6.0, p = 0.14). However, New Zealand infants were breast fed more frequently and for longer than infants in SWT, which would tend to reduce the risk of SIDS in the New Zealand population. In combination the differences in the prevalences of these four risk factors explain only 20% of the excess risk of SIDS in New Zealand.

CONCLUSIONS

The high SIDS mortality rate in New Zealand is not simply explained by a high prevalence of known and modifiable risk factors for SIDS.