You're asking about a condition called vasa previa. Although this condition is similar in some ways to placenta previa (in which the placenta is implanted low in the uterus when it should be implanted high in the uterus), it is actually in a different classification than placenta previa. In vasa previa, the umbilical cord is attached to the placenta in an unusual way, and the umbilical cord is also lying over the opening to the cervix. This occurs in about 1 in 5,000 pregnancies, and no one really knows why it happens. It's true that if you have this condition a cesarean birth might be necessary, for labor can cause a vasa previa to bleed and this would be disastrous for the baby. Be sure to stay in touch with your health care provider, and report any vaginal bleeding promptly. You'll probably be monitored more frequently during pregnancy than if you did not have a vasa previa, and you might be asked to restrict your activity. One very important thing for you to know is that your cervix should not be examined unless special precautions are taken to prevent bleeding.Therefore, if you should ever find yourself in a situation where you need to be seen by a physician who doesn't know you (in an Emergency Room, for instance, or in a strange city you might be visiting), you and your family should immediately tell the physician that you've been diagnosed with a vasa previa. Don't allow anyone to examine you vaginally unless preparations have been made for an immediate cesarean delivery if that becomes necessary. You are the best advocate for you and your family, so be sure to speak up! Best of luck with your pregnancy.