Objectives Despite the passage of state laws promoting breast feeding, a formal evaluation has not yet been conducted to test whether and/or what type of laws may increase breast feeding. The enactment of breastfeeding laws in different states in the USA creates a natural experiment. We examined the impact of state breastfeeding laws on breastfeeding initiation and duration as well as on disparities in these infant feeding practices.

Methods Using data from the Pregnancy Risk Assessment Monitoring System, we conducted differences-in-differences models to examine breastfeeding status before and after the institution of laws between 2000 and 2008 among 326 263 mothers from 32 states in the USA. For each mother, we coded the presence of two types of state breastfeeding laws. Mothers reported whether they ever breast fed or pumped breast milk (breastfeeding initiation) and, if so, how long they continued. We defined breastfeeding duration as continuing to breast feed for ≥4 weeks.

Results Breastfeeding initiation was 1.7 percentage points higher in states with new laws to provide break time and private space for breastfeeding employees (p=0.01), particularly among Hispanic mothers (adjusted coefficient 0.058). While there was no overall effect of laws permitting mothers to breast feed in any location, among Black mothers we observed increases in breastfeeding initiation (adjusted coefficient 0.056). Effects on breastfeeding duration were in the same direction, but slightly weaker.

Conclusions State laws that support breast feeding appear to increase breastfeeding rates. Most of these gains were observed among Hispanic and Black women and women of lower educational attainment suggesting that such state laws may help reduce disparities in breast feeding.