The latest data from the Office for National Statistics (ONS) shows that there were 183 unexplained infant deaths in England and Wales in 2017, a fall of 19% from the 226 in 2016 and the lowest level since records began in 2004.
The unexplained infant mortality rate also fell to its lowest level on record, dropping from 0.50 deaths per 1,000 live births in 2004 to 0.27 in 2017.
Rabiya Nasir, from the ONS, said: “The rate at which babies died from an unexplained cause before their first birthday fell to the lowest level on record in 2017 – almost halving since records began in 2004.
“The new low comes after our last set of figures showed an increase between 2015 and 2016, and re-establishes the long-term trend.
“The fall in unexplained deaths may be due to factors such as fewer expectant mothers smoking and more awareness of safer sleeping practices.”
The figures include deaths among children less than one year old from sudden infant death syndrome (SIDS) and when no medical cause can be recorded.
SIDS is the sudden, unexpected and unexplained death of an otherwise seemingly healthy baby.
The exact cause of SIDS is unknown, but maternal smoking during pregnancy, exposure to tobacco smoke, overheating and an unsafe sleeping environment have been linked to unexplained infant deaths.