Number of Pronuclei and Ploidy in IVF/ICSI–Derived Embryos
The 1PN zygotes can form by parthenogenesis, and will be haploid, or more commonly as a result of either premature pronuclear fusion or asynchronous pronucleus formation, and will be diploid (46 to 80 percent). These diploid zygotes can be identified in time-lapse culture as the dynamics of pronuclear appearance and merging are observable along with polar-body extrusion events that may be missed during standard fertilization checks. To accurately determine the type of 1PN present and ascertain whether a zygote has normally fertilized, some authors have utilized fluorescent in situ hybridization (FISH) techniques to look for the presence of a Y chromosome.2-5
Figure 8.1 illustrates an oocyte inseminated by ICSI which extrudes the second polar body at 2.1 hours post insemination (hpi) but appears to be unipronucleate.