During pregnancy, both the mother and fetus are vulnerable to environmental pollution by particulate matters and chemicals. Although the toxicity of free pollutants has been frequently reported, the impact of nanoparticle/pollutant adducts on the vulnerable pregnant population remains unclear. In this study, pregnant mice were orally exposed to Mg(OH)(2) nanoflakes and nanoflakes adsorbed with Cr(VI) anions during the pen-implantation and organogenesis stages of pregnancy at doses that did not induce systemic toxicity or pregnancy complications. The nano-Mg(OH)(2)/Cr(VI) adducts formation reduced fetal developmental toxicity compared with the toxicity induced by the same concentration of free Cr(VI) anions. (C) 2015 Elsevier B.V. All rights reserved.