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A Tokyo clinic has developed a groundbreaking in vitro fertilization procedure in which sperm from a third person is used to activate a sterile husband’s sperm during fertilization, according to the head of the clinic.

Osamu Kato, of Kato Ladies Clinic in Shinjuku Ward, said the technique involves first injecting another man’s sperm into a wife’s ovum to “lead the way” and later replacing them with the husband’s sperm cells in order to attain fertilization.

Kato said the technique can be “a tremendous boon” for men with low sperm counts, adding that he expects to soon report his clinical findings to the Japan Society of Fertility and Sterility.

But because the technique deviates drastically from the conventional method of in vitro fertilization, other scientists may take a dim view of the new technique, especially from an ethical standpoint, sources familiar with in vitro fertilization said.

The procedure utilizes a husband’s round sperm cells — immature cells whose growth has stopped immediately before growing into full-size sperm inside the testis.

Kato said he injects the donor’s sperm cells into the wife’s ovum by using an ultrafine glass tube. After confirming that the ovum has reached the stage where it can allow fertilization, he removes the donor’s sperm cells, which by then are in a pronucleus state.

Kato then places the husband’s round sperm cells into the ovum, thereby achieving fertilization between the resultant sperm cells and the ovum.

Kato said he has applied the technique to 11 couples and has been successful in nurturing five fertilized eggs to blastocyst — the stage immediately before the fertilized egg’s implantation — from four couples.

He said the fertilized eggs are now kept in a frozen state so they can be put back into the uterus at any time.