Application of the Pronuclear Scoring System for Predicting the Morphology and Ploidy of Early Human Embryos

Abstract

The efficiency of in vitro fertilization and embryo transfers into human uteri is low, because approximately 50% of embryos transferred into the uterine cavity are capable to continue their development. This situation has generated the problem of early diagnosis of embryo potential at the stage preceding the selection of morphologically and chromosomally good quality blastocysts. The fertilization quality was assessed 16–18 h after an intracytoplasmic sperm injection (ICSI) micromanipulation by the presence of pronuclei using Z-scores. We examined the size and the location of pronuclei relative to the cell center, the number of nucleoli, and their distribution. The best development and, respectively, the highest implantation potential were demonstrated by embryos developed from zygotes of the Z1 category. Zygotes Z2 and Z3 also formed AA quality blastocysts on day 5. None of the fertilized oocytes forming zygote Z4 developed into a viable embryo. We have established differences in the capability to form AA quality blastocysts between zygotes of categories Z1, Z2, and Z3 and the category Z4 as well as between categories Z1 and Z3. It has been found that the highest number of embryos in which the number of the studied chromosomes corresponded to the norm was formed from zygotes of Z1 and Z2 categories, and a significant difference in the number of embryos in which aneuploidy has not been diagnosed has been found in embryos formed from zygotes of Z1, Z2, and Z3 categories compared with type Z4 zygotes.