There was a fall in the number of sudden infant deaths in England and Wales last year, according to the Office for National Statistics.
Parents are advised to put babies to sleep on their backs
There were 175 deaths in 2003 - down from 192 the previous year. The overall death rate in terms of the number of births is down 13%.
But the Foundation for the Study of Infant Deaths has queried the fall.
The charity said the true figure may be higher because some deaths are not being classed as sudden infant deaths.
The number of babies dying from sudden infant death before they are 12 months old has fallen steadily in recent years.
This drop is attributed to the 'Back to Sleep' campaign, which was launched in 1991.
It advised parents to put babies to sleep on their backs and not on their fronts. Sudden infant deaths fell from 1,700 in 1986 to 395 in 1998.
Earlier this year, the Department of Health published new advice warning parents not to sleep in the same bed as their baby.
It followed a study suggesting that it could increase the risk of sudden infant death.
These latest figures show that some parts of the population are more likely to experience sudden infant death than others.
In 2003, the babies of mothers under the age of 20 were almost twice as likely to die from cot death compared to the population as a whole.
Death rates for babies born outside marriage where only the mother registered the birth was four times higher than for babies born inside marriage.
Babies with fathers in routine and manual occupations were three times more likely to die compared to those in managerial and professional occupations.
However, the Foundation for the Study of Infant Deaths said the overall figures may not be accurate.
"ONS figures do not include sudden infant deaths whose cause is registered as 'unascertained'," it said in a statement.
"Whereas Scotland and Northern Ireland do include 'unascertained' deaths in the SID category, ONS excludes them."
It said the total number of sudden unexpected deaths in 2003, including those categorised as unascertained, was 342.
Joyce Epstein, its director, called for the system to be changed.
"There needs to be better consistency and agreement about sudden infant deaths and the labels used by different agencies and professionals to describe these deaths."
The figures also show that there are variations in infant mortality rates across England and Wales.
For instance, babies born in Birmingham and the Black Country are two and a half times more likely to die compared with those born in Dorset, Somerset, Hampshire or the Isle of Wight.