Introduction: Periconceptional supplementation with multivitamins containing folic acid reduces the risk of congenital malformations. We have previously investigated the effect oil the murine development of a multiple retinoic acid competitive antagonist, Bristol-Myers-Squibb 189453, showing that treated fetuses were affected with heart defects, thymus aplasia or hypoplasia, and severe anomalies of the central nervous system. Hereby, we analyzed the effects of nutritive therapy involving folic acid and methionine on teratogen-induced congenital defects in mice. Materials and methods: A total of 132 outbred CD1 litters were Studied. Pregnant mice were divided into four experimental groups, and an oral supplementation of H(2)O or folic acid, or methionine, or folic acid+methionine,vas administered from 0.5 days postcoitum until the end of pregnancy. At 7.5 days postcoitum, mice from all these groups were administered Bristol-Myers-Squibb 189453 to induce the teratogenic effect. At the end of pregnancy, fetuses were dissected and tissues were analyzed by histology and flow cytometric assays. Results: Folic acid reduces congenital heart diseases from 81.3% to 64.8%, neural tube defects from 20.3% to 3.7%, and thymus abnormalities from 98.4% to 27.8%, restoring a normal number of differentiated thymus cells. Methionine is less effective in contrasting congenital heart diseases and neural tube defects, and induces thymus cell proliferation but not differentiation. Folic acid+methionine weakly reduce congenital heart diseases and neural tube defects, but consistently reduce the incidence of fetuses affected with thymus pathologies from 98.4% to 67.7%. Conclusions: Our results suggest that folic acid and methionine periconceptional supplementations may influence the incidence of congenital defects and may probably induce negative selection of embryos presenting developmental anomalies. (C) 2009 Elsevier Inc. All rights reserved.