Birth weight by gestational age for Albertan liveborn infants, 1985 through 1998.

OBJECTIVES

(1) To provide percentile tables and graphs of birth weight by gestational age and by gender, for singleton and twin liveborn neonates. (2) To determine changes in birth weight relative to gestational age over the study period.

METHODS

Data on 556,775 singletons and 12,125 twins, born alive in Alberta from 1985 through 1998, were obtained from Alberta Registries - Vital Statistics. Mean birth weights for individual and grouped years were compared by independent two-tailed t-tests. Linear trends in birth weight over the 14-year period were obtained using one-way analyses of variance.

RESULTS

Four tables and corresponding graphs showing birth weight for gestational age by gender for 21 through 44 completed weeks gestation provide data for the 1st to 99th percentile. Changes in birth weight for the combined gestational ages included an increase for singletons (male, F 17.6, p < 0.001; female, F 53.3, p < 0.001), and a decrease for female twins (F 5.8, 0.004). The increase for singletons was seen at 38 through 42 weeks gestation for both genders. No change occurred under 38 weeks except in singleton females of 33 to 35 weeks with a decrease in birth weight observed from 2636 +/- 539 g, 1985 to 2576 +/- 479 g, 1998; t 2.5, p = 0.002.

CONCLUSIONS

The graphs and tables established in this study represent a specific geographic area and population. They may be relevant as a reference for other geographic regions and populations. The clinical significance of the observed increased birth weight among term, but not preterm newborns, requires critical evaluation.