Maternal experience of multiple hardships and fetal growth: Extending environmental mixtures methodology to social exposures

Abstract

Background: Women can be exposed to a multitude of hardships prior to and during pregnancy that may affect fetal growth, but previous approaches have not analyzed them jointly as social exposure mixtures.Methods: We evaluated the independent, mixture, and pairwise joint associations between self-reported hardships and birthweight and birthweight for-gestational age z-scores in the Chemicals in Our Bodies-2 prospective birth cohort (N=510) using G-computation. We examined financial hardship, food insecurity, job strain, poor neighborhood environment, low perceived social status, caregiving, stressful life events, and unplanned pregnancy collected via questionnaire administered in the second trimester of pregnancy. We used propensity score-based restriction to ensure our analyses had sufficient data support and estimated absolute differences in outcomes. Analyses were adjusted for maternal age, race/ethnicity, educational attainment, and pre-pregnancy body mass index.Results: Food insecurity and job strain were most strongly associated with reduced birthweight individually, with absolute differences of -155 g (95% confidence interval [CI] -316, 6) and -178 g (95% CI -347, -9), respectively. The pattern of association with birthweight for gestational age z-scores was similar for food insecurity, with an absolute difference of -0.20 (95% CI -0.49, 0.09), while the association for job strain was attenuated [-0.03 (95% CI -0.34, 0.28)]. Accounting for co-exposures resulted in similar findings. The pairwise joint effects on birthweight were strongest for food insecurity in combination with unplanned pregnancy [-305 g (95% CI -580, -29)] and stressful life events [-354 g (95% CI -612, -95)].Conclusions: Experiencing food insecurity and job strain during pregnancy may affect fetal growth, and experience of multiple hardships may exhibit stronger effects on this health outcome.