Babies born into larger families are far more likely to struggle to put on weight

An investigation into why some babies grow only very slowly in the first nine months of their lives has come to the conclusion that it has nothing to do with the prosperity of the parents.

But the new study has shown that babies born into larger families are far more likely to struggle to put on weight.

The findings come from 11,700 infants who are part of the Children of the 90s project based at the University of Bristol.

Researchers set out to investigate possible causes of Failure To Thrive - a term used by doctors to describe infants whose growth is substantially less than that of their peers.

Dr Pauline Emmett, Head of Nutrition at Children of the 90s says: "Not all infants grow well in the first year - and this very slow growth has been associated with problems in later life.

"We've looked very carefully at family characteristics and the growth of all the children to try to find out why some infants do not do as well as others" 

The 11,700 babies were weighed at birth, at six to eight weeks and at nine months. The study was most interested in the 5 per cent of children who put on least weight over that time.  

Previously it had been suggested that low socio-economic status was associated with poor growth. This was not borne out by this study. 

The main findings were:

• There is no association with socio-economic status. Babies born to parents in Social Class V (unskilled manual) are no more likely to be adversely affected than babies whose parents were classified as Social Class 1 (professional).
• There is a strong correlation between parental height and slow weight gain up to nine months.  Babies of short parents were eight times more likely to grow slowly when compared to babies with tall parents.
• Babies born into larger families are more likely to fail to thrive. Even a mother's second or third baby was more likely to fall into this group. A fourth child was twice as likely to fail to thrive. 

Dr Peter Blair the lead author said: "While it may not be surprising that babies of short parents are more likely to grow slowly, we are the first study to establish this association. Growth standards for future measurement need updating and parental height must be part of this new calculation. 

"We also found that babies in larger families are likely to grow more slowly. The reasons for this association are not clear and deserves more research."

The project is already investigating the growth and development of the children at 7 and 8 to assess the longer-term consequences of poor growth in the first year of life.