A teratogen is virtually any substance or event that can cause any type of birth defects during pregnancy. These prenatal defects can be both structural and psychological problems raging from very minor severity to death. The effect of teratogens on the baby is based on the period of pregnancy the mother is in. The three periods of fetal development include the zygotic, embryonic, and fetal period. The zygotic period spans from conception to two weeks. During this period there is rapid cell division and if there is a teratogenous effect, there can be a spontaneous abortion. The embryonic period lasts from the second to eight week. This is when major development takes place in the organs and body systems and there are beginnings of sensitivity. Since this is very early in development, the baby is at a great risk from teratogens and will have major structural problems. Sometimes this can be before the mother realizes she is pregnant which can be a huge problem for the baby. The last fetal stage continues from eight weeks until birth. The baby continues to develop physically, puts on fat, develops the brain and lungs, and has sensory and learning experiences. The baby will develop skills to help it be viable outside the womb. The effects of teratogens during this period can cause physiological defects and less severe structural problems. For example, there can be mental retardation, changes in how big the baby is, or incorrect lung development. .
Many legal, everyday substances may have teratogenic effects on a developing child without the mother even knowing. One such substance may be caffeine, which will be studied here. Caffeine is an important subject to study when looking at risks of defects or disorders on children because it is so commonly consumed. For example many mothers may be drinking a daily morning coffee or soda regularly throughout the day during their pregnancy.