But Mirfield had the lowest rates in the area for non-south Asian mums smoking throughout pregnancy.

While 18 per cent of mums-to-be in Mirfield continued smoking, figures for Dewsbury were almost double the national average and the worst in north Kirklees.

Authors of the report said south Asian mothers in the area had seemed reluctant to admit to smoking so the true number of pregnant women smoking could be even higher.

Dr Judith Hooper, director of public health for Kirklees, who headed the study, said: “I am shocked at the high numbers of women who smoked right through their pregnancy, leading to low birth-weight babies. I am also sure others will be as surprised as I was to learn that a new case of rickets – directly related to a mother’s lack of vitamin D – is diagnosed in this area every week.

“These factors, along with much of the information gathered, point heavily towards malnutrition in the mothers before, during and after giving birth.”

Infant deaths in North Kirklees, published by the Kirklees Primary Care Trust on Wednesday, investigated all 106 infant deaths in the district between 2002 and 2005 to identify factors that might contribute to the increasingly high local rates.

It follows statistics in 2005 that revealed the rate of babies in north Kirklees dying before their first birthday was at least 50 per cent higher than the national average, with Dewsbury highest in the district.

But Mirfield had the lowest infant death rate in north Kirklees and the lowest rates for low birth weight, an indicator of maternal health and nutrition before and during pregnancy.