Decreased term and postterm birthweight in the United States: impact of labor induction

OBJECTIVE: We sought to assess recent trends in falling mean birth-weight (BW) and gestational age (GA) among US non-Hispanic white singleton live births >= 37 weeks of gestation and the contribution of increased rates of induction to these trends. STUDY DESIGN: This was an ecological study based on US vital statistics from 1992 through 2003. RESULTS: From 1992 through 2003, mean BW fell by 37 g, mean GA by 3 days, and macrosomia rates by 25%. Rates of induction nearly doubled from 14% to 27%. Our ecological state-level analysis showed that the increased rate of induction was significantly associated with reduced mean BW (r = -0.54; 95% confidence interval [CI], -0.71 to -0.29), mean GA (r = -0.44; 95% CI, -0.65 to -0.17), and rate of macrosomia (r = -0.55; 95% CI, -0.74 to -0.32). CONCLUSION: Increasing use of induction is a likely cause of the observed recent declines in BW and GA. The impact of these trends on infant and long-term health warrants attention and investigation.