Teratogens are harmful chemicals or viruses that can be transferred from a pregnant mother to her developing fetus when exposed to teratogens which affect pregnancies and cause complications such as preterm labor, spontaneous abortion or miscarriages. Example of teratogen chemicals or viruses are; alcohol, tobacco smoke, mercury, lead, air pollution, pesticides, and drugs used during pregnancy. These toxicants cause low birth weight, paralysis, anemia, heart and lung problems to infants.