Are babies getting bigger? An analysis of birthweight trends in New South Wales, 1990-2005

Objective: To determine whether the proportion of babies born large for gestational age (LGA) in New South Wales has increased, and to identify possible reasons for any increase. Design and setting: Population-based study using data obtained from the NSW Midwives Data Collection, a legislated surveillance system of all births in NSW. Participants: All 1273924 live-born singletons delivered at term (>= 37 complete weeks' gestation) in NSW from 1990 to 2005. Main outcome measures: LGA, defined as > 90th centile for sex and gestational age using 1991-1994 Australian centile charts; maternal factors associated with LGA were assessed using logistic regression. Results: The proportion of babies born LGA increased from 9.2% to 10.8% (18% increase) for male infants and from 9.1% to 11.0% (21% increase) for female infants. The mean birthweight increased by 23 g for boys and 25 g for girls over the study period. Increasing maternal age, higher rates of gestational diabetes and a decline in smoking contributed significantly to these increases, but did not fully explain them. Conclusions: There is an increasing trend in the proportion of babies born LGA, which is only partly attributable to decreasing maternal smoking, increasing maternal age and increasing gestational diabetes.