Birth Defects No one is immune to birth defects, yet not everyone is equally susceptible. Birth defects are not merely a medical problem. They have profound effects on the social and psychological well being of their family and friends. In the normal course of fetal development, cells migrate to their appropriate destination so that organs and limbs form where they should. Usually, the genes perform flawlessly, but mistakes can and do occur. Some of the most common birth defects results from the interaction between one or two abnormal genes out of 100,000 that make up who we are. This is caused by the genes parents pass