Do population-based interventions widen or narrow socioeconomic inequalities? The case of breastfeeding promotion

Background: Despite numerous population-based randomized intervention trials, the impact of such interventions on socioeconomic inequalities has rarely been examined. We used data from a large cluster-randomized trial to assess the impact of a breastfeeding promotion intervention on socioeconomic inequalities in breastfeeding (exclusivity and duration) and in child cognitive ability at early school age. Methods: The Promotion of Breastfeeding Intervention Trial (PROBIT) randomized 31 Belarusian maternity hospitals and their affiliated polyclinics either to receive a breastfeeding promotion intervention modelled on the WHO/UNICEF Baby-Friendly Hospital Initiative or to continue the standard practices in effect at the time of randomization. We estimated and compared inequalities in discontinuation of exclusive breastfeeding before 3 months and of any breastfeeding before 12 months and in child verbal IQ at age 6.5 years, across maternal education strata between the two intervention arms. Findings: Socioeconomic inequalities in discontinuing exclusive breastfeeding before 3 months were negligible in the control group. However, graded inequalities by maternal education emerged in the intervention group {relative risk [RR] = 1.12 [95% confidence interval (CI): 1.04, 1.20] for partial university and RR = 1.20 [95% CI: 1.11, 1.31] for secondary education or less vs complete university; risk difference [RD] = 0.06 [95% CI: 0.03, 0.09] and 0.10 [95% CI: 0.06, 0.14], respectively}. For discontinuing any breastfeeding before 12 months, small socioeconomic gradients in the control group were widened in the intervention group (RR = 1.04 and 1.16, respectively, for mothers with secondary education or less). Despite these differential effects on breastfeeding, however, we observed a small, nonsignificant reduction in socioeconomic inequalities in child verbal IQ at age 6.5 years. Conclusions: A population-based intervention to promote breastfeeding slightly widened socioeconomic inequalities in breastfeeding but not those in child cognitive ability.