Maternal demographic characteristics and rates of low birth weight in Canada, 1961 to 1990.

Vital statistics on live births were used to examine trends in the demographic characteristics of mothers and rates of low birth weight (LBW) (under 2,500 grams) among children born to residents of Canada (excluding Newfoundland) from 1961 to 1990. The total number of live births with known birth weight declined from 458,000 in 1961 to 397,000 in 1990 (-13%). Over those three decades, the number of LBW infants dropped from 33,100 to 22,000 (-34%), and the proportion of live births accounted for by LBW infants (LBW rate) fell from 7.2% in 1961 to 5.5% in 1990 (-24%). An infant's birth weight is related to the mother's health and socio-economic environment. In urban Canada, the LBW rate was about 1.4 times higher in the lowest income neighbourhoods than in the highest. It was also higher among unmarried mothers than their married counterparts (7.3% vs. 5.0% in 1990), and greater among teenage mothers than those aged 20 to 34 (6.7% vs. 5.4% in 1990). The LBW rate was higher among first-borns than second children (6.0% vs. 4.9% in 1990). From 1961 to 1990, the proportion of births occurring outside marriage rose (especially in Quebec), as did the proportion of mothers of "parity 1" (those giving birth to their first child). Conversely, the proportion of births to teenage mothers declined. The LBW rate generally dropped across all maternal demographic characteristics examined, and in every region, over the period studied. The strongest decline was among unmarried mothers (from 11.3% in 1961 to 7.3% in 1990). By region, Quebec had consistently higher LBW rates than the other three regions. However, Quebec's LBW rate declined dramatically between 1961 and 1990, especially among unmarried mothers (from 13.8% to 7.5%). The LBW rate, standardized to the 1961 distribution of maternal age, parity and marital status, declined from 7.2% in 1961 to 5.1% in 1990 (-29%). By 1990, Quebec's standardized LBW rate (5.2%) was very close to the Canadian average (5.1%), while the Maritimes had the highest standardized LBW rate (5.3%). Thus, after standardization there was an almost complete reversal of the regional ranking which had prevailed in 1961.