Teratology is the study of birth defect and the word comes from a Greek word teras meaning monsters. It has a rich history of myth, folklore and experimental evidence. With the advent of the germ theory by Weismann in 1880s and the rediscovery of the Mendel’s law in 1909, the genetic basis for birth defect was accepted. The first human epidemic of birth defect induced by an environmental agent, linked rubella virus infection to organ defect. Also physical and chemical agent have been studied and known to cause malformation as evident with the thalidomide crises in 1960s. Cassava (Manihot esculenta crantz) is an important staple and cheap dietary source of calories for 200-300 million people in the tropics, however its nutritional usefulness is hampered by the presence of toxic cyanogens in its tuber(cortex). Cyanogenic glycosides are phytotoxins which occur in at least 2000 plant species that serves as food in developing society, Cassava been one of these foods containing cyanogenic glycosides. In other to evaluate the potentials of cassava induce teratogenicity and subsequently establish its minimum consumption during gestation fifty female Wister rats were used after determination of conception by cervical smear analysis. Ten per group, comprising of three tests and two control groups (positive and normal control). Cyanide was quantitatively calculated in the cultivars and free cyanide was determined by adapting the method of Smith described by Winton and Winton (1985), which is based on colorimetric reaction of picrate solution while the standard curve was established with potassium cyanide. A dose of 40mg, 80mg, and 160mg/kg of potassium cyanide equivalent of the extract was administered by gastric gavage during the 6th to 17th day of gestation. Litters were examined for gross defect and the parents were sacrifice by cervical dislocation after isofluran anesthesia. The research protocol underwent ethical scrutiny through our Department, Faculty and College ethical committee review process and was finally granted approval. There were multiple still births and resorption sites in the uterus of experimental groups. Retained dead fetus reveals distorted morphology with several visceral perforations. However litters did not show gross malformation. These findings suggest that cassava induce embyotoxicity occur during early development but litters who escape the toxic effect during early embryogenesis develop resistance probably due to adaptation and genetic variability.