An observational study using clinical case records has found a ten-fold increased risk of sudden unexpected death in infancy (SUDI) in siblings of SUDI cases.

The Care of Next Infant (CONI) programme in the UK maintains a database of infants of families where there has been a previous SUDI. Data were analysed on liveborn infants born, and enrolled on the CONI database, between 2000 and 2015. CONI provides support to families who have experienced SUDI in caring for their subsequent children through enhanced health visitor contact, provision of apnoea monitors, basic life support training, symptom diaries and weight charts.

There were 6,608 infants registered on the CONI database during the study period, including 171 who were first born infants to mothers whose male partner had previously had an unexplained infant death.

There were 29 unexpected infant deaths following the index death. These deaths occurred in 26 families; 23 with two deaths and three with three deaths. In each case the first death had been in an infant born to the same mother.

The cause of death was unexplained for 19 first and 15 CONI deaths. Accidental asphyxia accounted for two first and six CONI deaths; medical causes for three first and four CONI deaths; and homicide for two first and four CONI deaths. There were child protection concerns in ten families.

The SUDI rate for infants born in families with one previous SUDI was 3.93 (95% CI: 2.7-5.8) per 1,000 live births. The risk of a third death in a family with two previous cases of SUDI was 115 (95% CI: 40-290) per 1,000 live births.

When deaths caused by asphyxia, homicide and medical causes were excluded, this gave an unexplained infant death rate for infants born in families with a previous SUDI of 2.27 (95% CI: 1.4-3.7) per 1,000 live births.

Potentially modifiable risk factors for SUDI include maternal smoking before and after the birth; maternal mental health problems; unsafe sleeping practices such as the parent sharing a bed or sofa with the infant; and child abuse/neglect.

There were concerns about child abuse or poor parenting in more than half of CONI deaths. Most mothers smoked in pregnancy, and a third of CONI cases died in hazardous co-sleeping situations.

This study concluded that repeat SUDI within families is rare, with only 29 deaths reported in 26 families over a 16-year period. However, the repeat SUDI rate of 3.93 per 1,000 live births is more than ten times higher than the UK rate of unexplained infant deaths of 0.31 per 1,000 live births in 2016 down from 0.43 per 1,000 live births in 2006. Covert homicide occurred in two families, and only became apparent following the second death.

There were limitations to this study because factors such as low birthweight and prematurity were not considered and entry onto the database was voluntary. 

The study authors conclude: ‘Although our findings should provide reassurance to professionals dealing with a sibling SUDI case about the small possibility of homicide, it is important not to be complacent.

‘The risk of repeat SUDI in a family is ten times that of the general population, reflecting both inherent genetic risks as well as environmental factors such as maternal smoking and unsafe sleeping.’

Dr Peter Saul