Teratogenicity or reproductive toxicity broadly refers to the occurrence of biologically adverse effects on the reproductive system that may result from chemical exposure to several environmental agents which is characterized by alterations to the female or male reproductive organs related to endocrine system, or pregnancy outcomes. Teratogenesis signifies the structural malformations during fetal development, in distinction from other kinds of drug induced fetal damage such as growth retardation, dysplasia(e.g. Iodine-deficiency-related goitre), or the asymmetrical limb reduction. The exposure of teratogenic chemical prior to conception, during prenatal or postnatal development leads to manifestations of developmental toxicity including the death of the developing organism, structural abnormality, altered growth, and functional deficiency[1].It is estimated that approximately 10%-15% of congenital structural anomalies are the result of the adverse effect of environmental factors on prenatal development . Factors comprise not only chemicals but also micro-organisms including infections, maternal conditions and diseases like diabetes and physical factors like radiations. Teratogens are toxic agents that cause abnormal development resulting in birth defects. Between 3% and 5% of children born in the United States are born with developmental defects. Of these, only 2% to 3% of them are classified as teratogen-induced malformations. However, 60-70% of all defects are of unknown origin-developmental toxicology is an expanding field and some of the unclassified defects may eventually be classified as teratogen-induced. Teratogenic substances do not affect each developing fetus in the same way. The fetus is most at risk during organogenesis (development of organs), which begins at about three weeks post-conception, and continues until the organs' defining characteristics have been achieved. The severity and type of the congenital malformation may vary with the duration of exposure and the specific teratogen. However, exposure to the same substance on different days in development can produce different defects. Many teratogens are fatal at high doses, causing miscarriage. Defects that present later, such as growth development and functional impairment, are harder to relate to teratogen exposure. In the time between birth and detection of impairment, exposure to other toxicants may have occurred, increasing the difficulty of identifying the responsible toxicant. PRINCIPLES OF TERATOLOGY : James Wilson (in 1959) proposed six principles of teratology. A simplified version of these is as follows: 1. Susceptibility to teratogenesis depends on the embryo's genotype that interacts with adverse environmental factors (G x E interaction). 2. The developmental stage of exposure to the conceptus determines the outcome. 3. Teratogenic agents have specific mechanisms through which they exert their pathogenic effects.