Embryonic development after microsurgical repair of polyspermic human zygotes.

Correction of polyspermy through pronucleus extraction in the absence of membrane relaxants was applied to 25 polyspermic human zygotes. Nine zygotes survived the procedure, and seven cleaved normally (two of which were fixed for chromosome analysis); two proceeded to compact and one cavitated. Eighteen of the polyspermic zygotes (14 with three pronuclei and 4 with four pronuclei) were obtained from zona pellucida-intact oocytes, and seven (1 five-pronucleate 3 four-pronucleate, and 3 three-pronucleate) from previously zona-drilled oocytes. Survival and cleavage occurred in all groups except in four- and five-pronucleate zona-drilled zygotes. Criteria used to identify male pronuclei were (1) pronucleus-associated sperm tails, (2) increased pronucleus size, and (3) greater distance (relative to female pronuclei) from the second polar body. Sperm tails were never seen and pronucleus size usually was identical. Therefore, the third criterion was used, although its reliability should be further evaluated. Until complete pronucleus removal techniques and reliable pronucleus selection criteria are perfected, embryo replacement after polyspermy correction could result in aneuploidy and molar pregnancy.