Prenatal lead exposure and fetal growth: Smaller infants have heightened susceptibility

Abstract

Background: As population lead levels decrease, the toxic effects of lead may be distributed to more sensitive populations, such as infants with poor fetal growth.

Objectives: To determine the association of prenatal lead exposure and fetal growth; and to evaluate whether infants with poor fetal growth are more susceptible to lead toxicity than those with normal fetal growth.

Methods: We examined the association of second trimester maternal blood lead levels (BLL) with birthweight-for-gestational age (BWGA) z-score in 944 mother-infant participants of the PROGRESS cohort. We determined the association between maternal BLL and BWGA z-score by using both linear and quantile regression. We estimated odds ratios for small-for-gestational age (SGA) infants between maternal BLL quartiles using logistic regression. Maternal age, body mass index, socioeconomic status, parity, household smoking exposure, hemoglobin levels, and infant sex were included as confounders.

Results: While linear regression showed a negative association between maternal BLL and BWGA z-score (β=-0.06 z-score units per log2 BLL increase; 95% CI: -0.13, 0.003; P=0.06), quantile regression revealed larger magnitudes of this association in the <30th percentiles of BWGA z-score (β range [-0.08, -0.13] z-score units per log2 BLL increase; all P values<0.05). Mothers in the highest BLL quartile had an odds ratio of 1.62 (95% CI: 0.99-2.65) for having a SGA infant compared to the lowest BLL quartile.

Conclusions: While both linear and quantile regression showed a negative association between prenatal lead exposure and birthweight, quantile regression revealed that smaller infants may represent a more susceptible subpopulation.

Keywords: Birth weight; Fetal growth; Lead; Pregnancy; Quantile regression; Small-for-gestational age.

Copyright © 2016 Elsevier Ltd. All rights reserved.

Figures

Figure 1. Empirical distribution of birthweight-for-gestational age and associated predicted distributions assuming a log2 increment in maternal blood lead levels

This figure illustrates the empirical (solid line) and predicted (dashed and dotted lines) distributions from the association of prenatal lead exposure and birthweight-for-gestational age z-score as calculated by both linear (top) and quantile (bottom) regression assuming a range of five increments (log2) in maternal blood lead levels. Quantile regression estimates revealed that prenatal lead exposure is associated with a heterogeneous shift to left of the birthweight-for-gestational age z-score distribution, increasing in particular the probabilities infants would have been diagnosed as SGA or had lower birthweight-for-gestational age z-scores, had they been exposed to higher levels of lead prenatally.