Maternal Employment and Infant BMI z Score in a US Birth Cohort

Abstract

Objective: The purpose of this study was to investigate the association between maternal employment and infant BMI z score.

Methods: Longitudinal data from 520 mother-infant dyads participating in the Nurture Study, an observational cohort in the southeastern United States, were leveraged. Women were categorized as employed or nonemployed at 3, 6, 9, and 12 months, and measured anthropometrics were used to calculate infants' BMI z scores at the corresponding time points. BMI z score was defined using the World Health Organization standard. Household income was an effect modifier. Therefore, income-stratified (≤$40,000/y vs. >$40,000/y) linear regression models, with individual fixed effects, were used to examine associations between change in maternal employment status and BMI z scores among infants aged 3 to 12 months. Fixed effects controlled for time-invariant confounders (race/ethnicity, infant gender). This study also controlled for marital status and infant age.

Results: More women from higher-income (68.4%) versus lower-income households (52.6%) were employed. Among lower-income households, change from nonemployment to employment was associated with higher infant BMI z scores (β = 0.12; 95% CI: -0.01 to 0.25, P = 0.07). Among higher-income households, change in maternal employment status was associated with lower infant BMI z scores (β = -0.72; 95% CI: -1.17 to -0.27, P = 0.02).

Conclusions: Maternal employment was related to infant adiposity. The direction of the association varied by household-level income.

Figure 1

Mean BMI z score by employment status over time. BMI z score was defined using the World Health Organization standard. Employment status was measured at each time point. Nonemployed category combines women who were not employed and not looking for work with those not employed but looking for work. Employed category combines women who reported they were currently employed and those reporting they were employed, but on maternity leave.

Figure 2

Mean BMI z score by employment status and household income over time. BMI z score was defined using the World Health Organization standard. Nonemployed category combines women who were not employed and not looking for work with those not employed but looking for work. Employed category combines women who reported they were currently employed and those reporting they were employed but on maternity leave.