More importantly, the SNP rs4880 in SOD2 (AG & GG vs. AA) and higher Cd exposure showed a multiplicative-scale interaction on NTD risk, and the SNP rs1801133 in MTHFR (CT and TT vs. CC) and higher Cd exposure exhibited an additive-scale interaction on NTD risk, supporting an environmental-genetic interaction in the etiology of NTDs. This evidence concerns the gene MTHFR and neural tube defect.