Child marriage, maternal serum metal exposure, and risk of preterm birth in rural Bangladesh: evidence from mediation analysis

BACKGROUND: The prevalence of preterm birth in Bangladesh is estimated to be 19.1%, the highest in the world. Although prenatal exposure to several metals has been linked with preterm birth, fewer prospective studies have investigated the socioeconomic factors that affect metal exposure, leading to preterm birth risk. OBJECTIVE: We aim to identify novel metal biomarkers and their critical exposure windows, as well as the upstream socioeconomic risk factors for preterm birth in rural Bangladeshi, to shed light for future interventional strategies. METHODS: This study included data from 780 mother–offspring pairs, who were recruited to participate in a prospective birth cohort in Bangladesh (2008–2011). Serum concentrations of 19 metals were measured in the first and second trimesters using inductively coupled plasma mass spectrometry. Mediation analysis was performed to explore the upstream socioeconomic factors that affect the risk of preterm birth mediated via metal exposure concentrations. RESULTS: Early pregnancy exposure to serum zinc, arsenic, and strontium and mid-pregnancy exposure to barium were significantly associated with risk of preterm birth. Furthermore, younger marriage age was associated with an exponential increase in the risk of preterm birth, and women who married after 18 years old had a considerably lower risk of preterm birth. Mediation analysis indicated that these four elements mediated 30.2% of the effect of marriage age on preterm birth. CONCLUSION: This study indicated that maternal serum metal exposure mediates the impact of child marriage on the increased risk of preterm birth via metal exposures. The findings shed light on the mechanisms underlying such association and provide insights into future interventional strategies.