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

BackgroundStunted 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.MethodsA 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\u2009weeks’ post-partum (n\u2009=\u20091161). 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.ResultsDuring 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\u2009=\u2009−\u20090.67 [−\u20091.06; −\u20090.28], β\u2009=\u2009−\u20090.97 [−\u20091.51; −\u20090.48]; and β\u2009=\u2009−\u20090.87 [−\u20091.33; −\u20090.45], 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 −\u20090.35 [−\u20090.53; −\u20090.16]. The indirect effect of maternal BMI on infant LAZ was −\u20090.06 [−\u20090.08; −\u20090.03], revealing that 16% (−\u20090.06/−\u20090.35) of the relationship between cotton harvesting and infant LAZ, after adjustment, was mediated via maternal BMI.ConclusionThese 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.