From 1997 to 2003, about 30 children worldwide were born using a method that injected donor mitochondria DNA into eggs after they were fertilized. The first baby born with this technique was reported in 1997. In 2003, though, the FDA told fertility clinics that genetically manipulated embryos were considered a biological product, and subject to regulation, essentially halting the technique in humans.

The process of producing a three-parent baby involves taking the nucleus of one egg and inserting it into the cytoplasm of another egg which has had its nucleus removed, but still contains mitochondrial DNA, and then fertilizing the hybrid egg with a sperm. The purpose of the procedure is to remove a nucleus from a cell with defective mitochondria and place it in a donor cell with healthy mitochondria, which after fertilization will contain a nucleus with genetic material from only the two parents.[5]

The nucleus of a somatic cell is removed and kept, and the host's egg cell nucleus is removed and discarded. Now we have a lone nucleus and an empty (or deprogrammed) egg cell. The lone nucleus is then fused with the 'deprogrammed' egg cell. After being inserted into the egg, the lone (somatic-cell) nucleus is reprogrammed by the host egg cell. The egg, now containing the somatic cell's nucleus, is stimulated with a shock and will begin to divide. After many mitotic divisions, this single cell forms a blastocyst (an early stage embryo with about 100 cells) with almost identical DNA to the original organism. The technique of transferring a nucleus from a somatic cell into an egg that produced Dolly was an extension of experiments that had been ongoing for over 40 years. In the simplest terms, the technique used to produce Dolly the sheep – somatic-cell nuclear transplantation cloning – involves removing the nucleus of an egg and replacing it with the diploid nucleus of a somatic cell.