Prediction of dystocia by entanglement (impaction) in vertex-vertex type twin delivery

We studied the fetal position in vertex-vertex type twins in 6 impaction cases and in 23 cases of vaginal deliveries without impaction. The results obtained were as follows: (1) In 6 impaction cases, the presenting head of the first fetus was shown to be at the maternal pubic side and the head of the second fetus at the maternal sacral side. (2) In 23 cases without impaction, the presenting head of the first fetus was shown to be at the maternal sacral side and the head of the second fetus at the maternal pubic side. (3) There was a statistical significant difference between the 6 impaction cases and the 23 non impaction cases as determined by the Chi-square test (p < 0.001). Our study suggests that it is possible to predict the occurrence of impaction in vertex-vertex type twin deliveries by examining the positional relationship of the presenting heads of the first and second fetuses. There was a higher possibility of impaction when the head and body of twin 1 was located in the maternal-pubic position, while the head of twin 2 was in the sacral position. In contrast, impaction never occurred when the head and body of twin 1 was in the maternal-sacral position and the head of twin 2 was in the pubic position.