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

Objective

We sought to assess recent trends in falling mean birthweight (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.

Key words: birthweight, cesarean section, ecological analysis, gestational age, labor induction, vital statistics