Bed sharing, maternal smoking raise sudden unexpected death in infancy risk

02 June 2017

The combination of bed sharing and maternal smoking is extremely hazardous for infants, giving rise to a 32-fold increase in the risk of sudden unexpected death in infancy, new research has found.

The study, called “SUDI Nationwide Study”, published in the New Zealand Medical Journal, involved a three year nationwide case-control study carried out between 1 March 2012 and 28 February 2015 by a team of researchers led by the University of Auckland.

“Despite a major reduction in overall infant mortality, sudden unexpected death in infancy (SUDI) continues to be of concern in New Zealand, as the rate is high by international standards, and is even higher in Māori,” says lead researcher, Professor Edwin Mitchell, of the University of Auckland.

The research comes after a previous three-year case-control study in 1987-1990 which examined risk factors for sudden infant death syndrome (SIDS), known as the New Zealand Cot Death Study.

“Our study shows that many of the risk factors that were identified in the original New Zealand Cot Death Study are still relevant today,” says Professor Mitchell.

“The combination of maternal smoking in pregnancy and bed sharing is extremely hazardous for infants.

“Furthermore, our findings indicate that the SUDI prevention messages are still applicable today and should be reinforced.”

There were 137 SUDI cases during the three years, giving a SUDI mortality rate of 0.76 per 1000 live births. The rate for Māori was 1.41/1000, Pacific 1.01/1000 and non-Māori non-Pacific (predominantly European) 0.50/1000.

SUDI occurred more frequently in male infants than female, and were more common in twins and those with a low birth weight. The peak age of death was one to three months.

The research suggests that SUDI mortality could be reduced to seven per year in New Zealand (approximately 1 in 10,000 live births).

The two major risk factors for SUDI were found to be maternal smoking in pregnancy (6-fold increased risk) and bed sharing (5-fold increased risk).

The combination of maternal smoking in pregnancy and bed sharing is extremely hazardous for infants, with a 32-fold increased risk.


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