Does blastocyst culture eliminate paternal chromosomal defects and select good embryos? Inheritance of an abnormal paternal genome following ICSI

Following intracytoplasmic sperm injection (ICSI), similar to 60-70% of ooc ytes are fertilized and of these embryos, similar to 45% withstand in-vitro culture conditions to produce healthy blastocysts. The efficiency of impla ntation of 2-4-cell embryos selected at the pronuclear stage and that of bl astocysts are comparable. However, prolonged selection of embryos in vitro (4-5 days), has been proposed to eliminate chromosomal abnormalities, more specifically those inherited by defective spermatozoa. This hypothesis is b ased upon the assumption that the paternal genetic contribution is indispen sable for blastocyst development, Here we examine this hypothesis and sugge st that phenotypic manifestation of paternal genomic abnormalities might no t occur prior to implantation, In addition to the parent-of-origin effect d uring embryogenesis, blastocyst transfer may not prevent the inheritance of genetic defects involving 'male factor' loci.