Therapeutic cloning: Cloning designed as therapy for a disease. In therapeutic cloning, the nucleus of a cell, typically a skin cell, is inserted into a fertilized egg whose nucleus has been removed. The nucleated egg begins to divide repeatedly to form a blastocyst. Scientists then extract stem cells from the blastocyst and use them to grow cells that are a perfect genetic match for the patient. The cells created via therapeutic cloning can then be transplanted into the patient to treat a disease from which the patient suffers. In contrast to the goal of therapeutic cloning, the goal of reproductive cloning is to create a new individual, an idea that has stirred great controversy and met with almost uniform disapproval.
Artificial embryo splitting or embryo twinning , a technique that creates monozygotic twins from a single embryo, is not considered in the same fashion as other methods of cloning. During that procedure, a donor embryo is split in two distinct embryos, that can then be transferred via embryo transfer . It is optimally performed at the 6- to 8-cell stage, where it can be used as an expansion of IVF to increase the number of available embryos.  If both embryos are successful, it gives rise to monozygotic (identical) twins .