Teratology: It is the study of abnormal embryos. In other words teratology is the study of abnormalities of physiological development. It is often use as the study of birth defects, but it is broader than that. Taking teratology in other developmental stages like as puberty or other life forms, such as plants. In all newborns birth defects are known to occur in 3-5%. There are the leading causes of infant mortality in the United States, accounting for more than 20% of all infant deaths. 

7 to 10% of all children will require extensive medical care to diagnose or treat a birth defect. It was previously thought that the mammalian embryo developed in the impervious uterus of the mother and it is protected from all extrinsic factors. After the thalidomide disaster of the 1960s, it has became apparent or more accepted that the developing embryo can be highly vulnerable to certain environmental agents which have negligible or non-toxic effects to adult individuals.