In the development process of the zygote formed by the fertilization of a single egg; If cell mass decomposition occurs late, after the 12th day, the cell groups that will form the fetus have begun to differentiate. With the separation of undifferentiated cell groups, whichever organ group it corresponds to, those organs become pairs. Cell groups that have already differentiated and developed to form tissues become partners with whichever organ they correspond to. This situation is called conjoined twins. There are some of the conjoined twins; Adhesion degrees can be determined while still in the mother’s womb. Therefore, it is possible to allow the continuation of pregnancy for those who can be separated after birth. However, in cases where the probability of successful separation surgery after delivery is very low, the pregnancy can be terminated.