Maternal BMI mediates the impact of crop-related agricultural work during pregnancy on infant length in rural Pakistan: A mediation analysis of cross-sectional data

Abstract

Background: Stunted growth in early infancy is a public health problem in low-And-middle income countries. Evidence suggests heavy agricultural work during pregnancy is inversely associated with maternal body mass index (BMI) and infant birth weight in low-and middle-income countries; but pathways linking agricultural work to length-for-Age Z-scores (LAZ) in early infancy have not been examined. This study aimed to investigate the relationship between agricultural work during pregnancy, post-natal maternal BMI and LAZ among young infants in rural Pakistan; and explored whether maternal BMI mediated the relationship between agricultural work and infant LAZ. Methods: A cross-sectional survey was conducted from December 2015 to January 2016 in rural Sindh, Pakistan. Mother-infant dyads were recruited via systematic random cluster sampling at 2-12 weeks' post-partum (n = 1161). Anthropometric measurements (maternal and infant height/length and weight) and questionnaire data were collected. Multivariable linear regression and structural-equation based mediation analyses were used to examine associations of agricultural work during pregnancy with maternal BMI and infant LAZ. Results: During pregnancy, women reported engaging in livestock-related work (57.0%), crop-related work (42.7%), and cotton harvesting (28.4%). All three forms of agricultural work were negatively associated with maternal BMI (β =-0.67 [-1.06;-0.28], β =-0.97 [-1.51;-0.48]; and β =-0.87 [-1.33;-0.45], respectively). Maternal engagement in cotton harvesting alone was negatively associated with infant LAZ after controlling for confounding factors. The total negative effect of cotton harvesting on infant LAZ was-0.35 [-0.53;-0.16]. The indirect effect of maternal BMI on infant LAZ was-0.06 [-0.08;-0.03], revealing that 16% (-0.06/-0.35) of the relationship between cotton harvesting and infant LAZ, after adjustment, was mediated via maternal BMI. Conclusion: These results underscore a need to reduce labour-intensive agricultural workload demands during pregnancy, especially in cotton harvesting, to reduce risks of negative maternal energy balance and poor growth outcomes in early infancy.