Purpose: To (i) investigate a possible association between different features of pronuclear (PN) morphology and different features of blastocyst morphology, (ii) evaluate the combination of PN and blastocyst morphologies as a predictive factor for ICSI outcomes and (iii) identify possible contributing factors to poor PN morphology.
Methods: This study included 908 normally fertilised zygotes reaching full blastocyst stage, obtained from 350 patients undergoing ICSI cycles, in which the implantations rates were 0 % or 100 %. The influence of PN morphology on blastocyst morphology and on the rates of pregnancy and miscarriage was investigated. Embryos were graded and split into three groups, taking into consideration both the PN and the blastocyst status. The pregnancy rate was compared among these groups.
Results: Inner cell mass (ICM) alterations were correlated with the number of nucleolar precursor bodies (NPB), while trophectoderm alterations were correlated with the size of the pronuclei and the distribution of the NPB. The distribution of the NPB had an impact on the chances of pregnancy. A significant difference was observed among the groups regarding the pregnancy rate. The maternal age, number of aspirated follicles and number of retrieved oocytes influenced the incidence of PN defects.
Conclusions: These findings suggest that a lower oocyte yield may lead to higher-quality PN zygotes. In addition, different PN features may influence further embryo development, especially the quality of the blastocyst. Moreover, the association between PN and blastocyst morphology may be used as a prognostic tool for implantation.