Microsurgical enucleation of tripronuclear human zygotes.

Polyspermic fertilization of human oocytes in vitro produces genetically abnormal embryos whose replacement in utero represents a potential obstetrical risk. Microsurgical removal of extra male pronuclei offers the possibility that normal ploidy can be restored in these zygotes. Pronuclear removal was attempted in three tripronuclear human oocytes fertilized in vitro. Male pronuclei were distinguished by their larger size and an associated sperm tail piece. Zygotes were pretreated with cytochalasin B and colcemid in phosphate-buffered saline before microsurgery. Enucleation was completed in all embryos; syngamy occurred in one embryo, but cleavage was not observed.