Maternal blood arsenic levels and associations with birth weight-for-gestational age

Background: Among highly exposed populations, arsenic exposure in utero may be associated with decreased birth weight, however less is known about potential effects of arsenic exposure in urban communities without contaminated sources such as drinking water. Objective: Investigate the association of blood arsenic levels with birth weight-for-gestational age categories within a prospective birth cohort study. Design/methods: We analyzed 730 mother-infant dyads within the Programming Research in Obesity, GRowth, Environment and Social Stressors (PROGRESS) cohort in Mexico City. Total arsenic was measured in maternal blood samples from the 2nd and 3rd trimesters, at delivery, as well as from infant umbilical cord blood samples. Multivariable, multinomial logistic regression. models adjusting for maternal age at enrollment, pre-pregnancy body mass index, parity, infant sex, socioeconomic position, and prenatal environmental tobacco smoke exposure were used to calculate odds ratios of small-for-gestational age (<10th percentile, SGA) and large-for-gestational age (>90th percentile, LGA) compared to appropriate-for-gestational age (AGA) per unit increase of log-transformed arsenic. Results: Median (IQR) blood arsenic levels for maternal second trimester were 0.72 (0.33) μg/L, maternal third trimester 0.75 (0.41) μg/L, maternal at delivery 0.85 (0.70) μg/L, and infant cord 0.78 (0.65) μg/L. Maternal delivery and infant cord blood samples were most strongly correlated (spearman r = 0.65, p < 0.0001). Maternal arsenic levels at delivery were associated with significantly higher odds of both SGA (adj. OR = 1.44, 95% CI: 1.08–1.93) and LGA (adj. OR = 2.03, 95% CI: 1.12–3.67) compared to AGA. Results were similar for cord blood. There were 130 SGA infants and 22 LGA infants. Earlier in pregnancy, there were no significant associations of arsenic and birth weight-for-gestational age. However, we observed non-significantly higher odds of LGA among women with higher arsenic levels in the 3rd trimester (adj. OR = 1.46, 95% CI: 0.67–3.12). Conclusion: We found that in a Mexico City birth cohort, higher maternal blood arsenic levels at delivery were associated with higher odds of both SGA and LGA. However, sources and species of arsenic were not known and the number of LGA infants was small, limiting the interpretation of this finding and highlighting the importance of future large studies to incorporate arsenic speciation. If our findings were confirmed in studies that addressed these limitations, determining modifiable factors that could be mitigated, such as sources of arsenic exposure, may be important for optimizing fetal growth to improve long-term health of children.