The social determinants of birthweight before and during the COVID-19 pandemic across 5 countries

Abstract Birthweight is associated with the social determinants of health and has long-term effects on health and socioeconomic outcomes. During crises like the COVID-19 pandemic, we may observe stronger effects of social determinants on birthweight because of the unequally shared socioeconomic and health-related burden across social strata. Importantly, if crises change the association between social determinants and birthweight, this may cause differences in social inequalities in life course outcomes between exposed and unexposed cohorts. We used register-based data covering births in Brazil, Ecuador, Finland, Spain, and the United States between 2015-2021. To estimate social inequalities in birthweight before and during the pandemic, we used multilevel analysis of individual heterogeneity and discriminatory accuracy. Strata were based on parental socioeconomic circumstances, maternal age, partnership status, and parity. In our analysis, we distinguished between exposed cohorts conceived before and during the pandemic. Across countries and periods, strata-covariates accounted for 1.5% to 3.2% of the variation in birthweight. Comparing unexposed births with those exposed to the pandemic in utero, change in social inequalities in birthweight measured by the variance partition coefficient ranged from +0.4%-points [95%CI:0;0.8] among male babies in Brazil to -0.3 [95%-0.5;-0.11] among male babies in Spain. Parental socioeconomic circumstances, maternal age, partnership status, and parity accounted for only 1.5% to 3.2% of the variation in birthweight across included countries with little to no change caused by the pandemic. Our results thus suggest that the pandemic has not noticeably changed social inequalities in birthweight. This indicates that in utero exposure to pandemic mitigation measures did not unequally affect birthweight despite the unequally distributed burden of the pandemic across social strata. Key messages • Before and during the COVID-19 pandemic, parental socioeconomic circumstances, maternal age, partnership status, and parity accounted for only 1.5% to 3.2% of the variation in birthweight. • Social inequalities in birthweight among in utero exposed births conceived before and during the COVID-19 pandemic did not change compared to babies born before the pandemic.