Babies of Asian families in the UK are still smaller at birth

Babies born in developing countries tend to be lighter at birth than babies born in more advantaged countries although within developing countries more affluent mothers have babies whose birthweights are similar to those of babies in the developed world. Emigration to a more advantaged country results in an increase in birthweights. Thus it has been estimated that the average birthweight of babies born in the UK to mothers born on the Indian subcontinent is about 300 g greater than that of babies born in India but about 300 g lighter than that of babies in general in the UK. The birthweight deficit is traditionally ascribed to environmental influences such as infection and poor diet. It is expected that birthweights in immigrant populations will reach those of the indigenous population within one or two generations. Data from Southampton, however, (BM Margetts, et al.

) suggest that that has not happened over the last 40 years for babies born to families who immigrated from the Indian subcontinent.

The study included data on 2395 singleton term births to South Asian mothers (identified by name) in Southampton since 1957. Some of the mothers were born outside the Indian subcontinent and birthweight tended to be greater for the babies of Muslim mothers and of mothers born in Pakistan or Fiji. Analysis of birthweight trends was restricted to the babies of 1435 mothers born on the Indian subcontinent (first generation) and 283 born in the UK (second generation). First generation mothers were older and heavier and had more children than second generation mothers. The girl babies of second generation mothers were significantly lighter at birth than those of first generation mothers (mean 2950 vs 3071 g) but there was no significant intergeneration difference in birthweights for boys. The low-birthweight rate was 7.5% (first generation) vs 11.7% (second generation). The differences between generations disappeared after adjustment for gender and mother's ethnic group, age, religion, parity, and weight at booking. There was no clear trend to increasing birthweight with time for either group after adjustment for factors known to influence birthweight. On multiple regression analysis year of birth was not shown to influence birthweight.

There has been no significant increase in birthweight over the last 40 years for the children of first or second generation mothers of families who immigrated from the Indian subcontinent to the UK. The reasons for persisting lower birthweight are not known but it can not be assumed that birthweights in this group will increase spontaneously with time.