Trends of abnormal birthweight among full-term infants in Newfoundland and Labrador.

Objectives: The objective of this study was to investigate whether any observed trends in birthweight are accompanied by changes in maternal sociodemographic characteristics, including age, marital status, and education.

Methods: We conducted a population-based study of term singletons born in Newfoundland and Labrador, Canada, between 1992 and 2005 (N = 66,638). Large-sample significance tests for two population proportions were used to test whether differences in mean birthweight, the proportion of low and high birthweight infants, and differences in maternal socio-demographic characteristics between 1992-95 and 2002-05 were statistically significant. Chi-square tests were used to test for associations between birthweight group and maternal age, education and marital status. Multivariate logistic regression was used to examine the interaction of these effects across time periods.

Results: Of the 66,638 infants included in the study, 54,256 (81.4%) were born in the normal birthweight range (2500-4000 grams) while 11,305 (17.0%) were high birthweight (> 4000 grams) and 1,077 (1.6%) were low birthweight (< 2500 grams). The rate of low birthweight significantly decreased from 1992 to 1995 compared to the period 2002 to 2005 (1.9% to 1.3%: p < 0.01). The rate of high birthweight significantly increased over the same two time periods (16.2% to 17.5%: p < 0.01). Mean birthweight increased from 3529 grams to 3566 grams (p < 0.01). Compared to women who had babies from 1992 to 1995, women who gave birth from 2002 to 2005 were more likely to be older, have higher levels of education, and never have been married. Birthweight outcomes were significantly associated with mother's age, education and marital status.

Conclusion: Changes in maternal demographics are associated with the upward shift in birthweight in Newfoundland and Labrador.