Birth Weight Distribution as an Indicator of Environmental Effects on Fetal Development

A medical birth registry was used for a geographical anal-ysis of birth weight distribution. Nearly 900000 Swedish singleton births, 1973-1981. were used for an analysis of the effect of some variables and for standardization for these variables. A marked change in the rate of low birth weight infants (LBW, <2500 g) was seen in the country between 1976 and 1977. A U-formed effect of maternal age and of parity was demonstrated. A marked interaction between the effects of these two variables existed. Two social groups were compared and the well-known high rate of LBW infants associated with low socioeconomic conditions was demonstrated. Standardization for the var-iables mentioned influenced this effect only little but re-duced the difference between the social groups concern-ing infants above 3.5 kg weight. The background dat