What are the effects of teratogens? Teratogens are chemicals or infectious agents that can cause severe birth defects in the conceptus by disrupting tissue and organ development. Teratogens may cause the conceptus to implant somewhere other than the uterus. Teratogens initiate the differentiation of the germ layers by promoting organogenesis. Teratogens will cause the placenta to attach close to the cervix, which may lead to the placenta hemorrhaging.