The non-linear association between low-level lead exposure and maternal stress among pregnant women

Background: Neuro-developmental impairments in the developing fetus due to exposure to low-level lead have been well documented. However, few studies have investigated the relation between maternal stress levels and low-level lead exposure among pregnant women. Objectives: To investigate the relation between maternal blood lead and stress levels during index pregnancy. Methods: 1931 pregnant women (gestational week 28-36) were investigated using stratified-cluster sampling in Shanghai in 2010. Maternal life event stress and emotional stress were assessed using "Life Event -Stress-Scale-for-Pregnant-Women" (LESPW) and "Symptom-Checklist-90-Revised" (SCL-90-R), respectively. Maternal whole blood lead levels were determined, and other data on covariates were obtained from maternal interviews and medical records. Two piecewise linear regression models were applied to assess the relations between blood lead and stress levels using a data-driven approach according to spline smoothing fitting of the data. Results: Maternal blood lead levels ranged from 0.80 to 14.84 mu g/dL, and the geometric mean was 3.97 mu g/dL. The P-values for the two piecewise linear models against the single linear regression models were 0.010, 0.003 and 0.017 for models predicting GSI, depression and anxiety symptom scores, respectively. When blood lead levels were below 2.57 mu g/dL, each unit increase in log10 transformed blood lead levels (mu g/dL) was associated with about 18% increase in maternal GSI, depression and anxiety symptom scores (P-GSI = 0.013, P-depression=0.002, P-anxiety=0.019, respectively). However, no significant relation was found when blood lead levels were above 2.57 mu g/dL (all P-values > 0.05). Conclusion: Our findings suggested a nonlinear relationship between blood lead and emotional stress levels among pregnant women. Emotional stress increased along with blood lead levels, and appeared to be plateaued when blood lead levels reached 2.57 mu g/dL. (C) 2016 Elsevier B.V. All rights reserved.