Dr. Kurt Benirschke, professor of Pathology and Reproductive Medicine, states that since the advent of sonography, the number of witnessed occurrences of a fetus spontaneously vanishing is now documented. These formerly existing but now vanishing twins or multiple-pregnancy fetuses had been identified only occasionally. The twins were ascertained mainly when pregnancies had incidental radiography, or when placentas were examined by a pathologist. In 1989, the term "Vanishing Twin" was mentioned by Elizabeth Noble who noted that the surviving fetus experiences grief, anger and despair. She estimated that in about 4% of all pregnancies, a co-twin dies at sometime without a trace. These deeply repressed memories of loss begin to emerge in various kinds of therapies. When such memories do surface, they witness what the co-twin was feeling at the time of the loss. Clearly though, vanished twins have always existed but they were not seen with any frequency until sonography became a practical tool. Sometimes when twins are recognized by sonography, one embryo truly vanishes and cannot be traced, even by skilled examination of the delivered placenta. S. Levi, who studied over 6,000 early pregnancies sonographically, found that of the 188 sets of twins identified, only 86 sets were delivered as twins. From this it was inferred that the others had "vanished." This means that there were twins but only a single one was born. The earlier the diagnosis of twins was made, the more frequently a twin apparently disappeared! The embryos of the dead twin may become incorporated into the placental membranes. The surviving twin may occasionally display congenital abnormalities. When one twin dies later in pregnancy and the gestation continues for sometime, the water of the dead twin's tissue may be reabsorbed and the dead fetus can become flattened from pressure of the growing twin. The most widely discussed consequence of twin death is the possible occurrence of widespread damage in a surviving twin not only physically but also emotionally. Dr David B Chamberlain, psychologist, states that the earlier a fetus, infant is subjected to pain, the greater the potential for harm. Pain makes deep impression on fetuses and babies. The younger the person the more impressionable and damaging the pain, anger, grief, loss may become.