Embryos with high implantation potential after intracytoplasmic sperm injection can be recognized by a simple, non-invasive examination of pronuclearmorphology

Embryos are conventionally selected for transfer based on the evaluation of the cleavage speed and extent of blastomere fragmentation. Here we examine d whether the predictive value of these criteria, as indicators of the chan ce of embryo implantation, can be further potentiated by adding previously described criteria reflecting the regularity of pronuclear development. In a group of embryos selected for transfer in 380 fresh embryo transfer cycle s according to the conventional criteria, the transfer of only those embryo s that developed from zygotes judged normal at the pronuclear stage (patter n 0) gave significantly higher pregnancy (44.8%) and implantation (30.2%) r ates compared with the pregnancy (22.1%; P < 0.05) and implantation rates ( 11.2%; P < 0.001) for the transfers of only those embryos that developed fr om zygotes judged abnormal (non-pattern 0). The transfer of only one patter n 0 embryo was sufficient for the optimal chance of pregnancy (no differenc es in pregnancy rates after transfer of one, two or three pattern 0 embryos ), whereas the transfer of two pattern 0 embryos mostly resulted in a twin pregnancy. The inclusion of the criteria based on pronuclear morphology can thus lead to the application of a single embryo transfer policy and optimi ze the selection of embryos for transfer and cryopreservation.