Objective: To characterize the effects of maternal arsenic exposure on birth weight.

Methods: Hair, toenail, and drinking water samples were collected from pregnant women (n = 52) at multiple time points during pregnancy and from their newborns after birth. Total arsenic was measured using inductively coupled plasma-mass spectrometry. The association between arsenic and birth weight was investigated using linear and logistic regression models.

Results: Maternal hair arsenic measured early in pregnancy was associated with decreased birth weight ([beta] = -193.5 +/- 90.0 g, P = 0.04). Maternal hair and drinking water arsenic levels measured at first prenatal visit were significantly correlated with newborn hair arsenic level ([rho] = 0.32, P = 0.04 and [rho] = 0.31, P = 0.04).

Conclusions: Results suggest that maternal arsenic exposure early in pregnancy negatively affects newborn birth weight and that maternal hair provides the best integrated measure of arsenic exposure.