This thesis examines the mechanisms by which teratogenic agents disrupt normal embryonic and fetal development. It reviews major categories of teratogens, including medications, infectious agents, environmental exposures, maternal conditions, and nutritional deficiencies. The molecular and pharmacological pathways underlying congenital malformations are discussed together with their effects on fetal organ development. Current prevention strategies, prenatal risk assessment, and evidence-based clinical recommendations are also evaluated. Overall, the thesis emphasizes that understanding teratogenic mechanisms is essential for minimizing fetal risk and improving maternal-fetal healthcare.