The number of babies dying in England and Wales has increased for the first time in four years and the West Midlands recorded the highest rate of fatalities.
Two of every three infant deaths occurred within the first month of life, according to figures released by the Office for National Statistics.
Conditions because of babies being born prematurely was the main cause of death (58 per cent), with congenital abnormalities causing 24 per cent of fatalities.
Doctors have blamed the rise on social factors, such as mothers' poor diet, smoking and alcohol use.
The practice of marrying relations, such as first cousins, in some cultures was also blamed for a rise in congenital abnormalities.
According to the figures, the mortality rate for infants under the age of one in England and Wales increased to
5.3 per 1,000 live births in 2003, from 5.2 in 2002. This is the first increase in the rate since 1999.
In the West Midlands, there were 7.4 deaths per 1,000 live births compared with 4.1 in the South-west, which had the lowest rate in England. The number of stillborn babies has also risen for the second successive year, to 5.7 stillbirths per 1,000 total births in 2003, from 5.6 in 2002 and 5.3 in 2001.
Mortality rates among babies was higher where the mother was born outside the UK or where the child was born outside marriage, the ONS said.
Dr Sam Ramaiah, director of public health for Walsall, said while Walsall had one of the lowest rates of infant mortality in the region, the death rate was an issue in the West Midlands.
He said: "I think it is due to the infections the babies acquire while they are developing and the second reason is due to congenital abnormalities.
"A lot is due to the mother's nutrition and also things like smoking and alcohol consumption.
"The other issue is interrelations between certain cultures, such as marrying close relations, which can lead to congenital problems. This is an issue relevant to the West Midlands."
The ONS also revealed there were 1,365 deaths of children aged between one and 14 in 2003, giving a death rate of 15 per 100,000 children - the same as in 2002.
The main causes was injury and poisoning (22 per cent) with cancer causing 21 per cent of fatalities.
"There is an issue that slightly older children are dying from accidents, either at home or outside, and obviously there are a lot more teenagers who die from motorbike accidents than from drugs," Dr Ramaiah added.