Pronuclear orientation, polar body placement, and embryo quality after intracytoplasmic sperm injection and in-vitro fertilization: further evidence for polarity in human oocytes?

Abstract

Three hypotheses were tested: (i) the distance between first and second polar bodies (PB) may relate to embryo morphology, (ii) that the orientation of pronuclei (PN) relative to PB may relate to embryo morphology, (iii) that the placement of a spermatozoon in a fixed plane relative to the first PB [intracytoplasmic sperm injection (ICSI)] may alter PN/PB orientation relative to in-vitro fertilization (IVF). A total of 251 two pronuclear (2PN) embryos (124 ICSI, 127 IVF) from 64 patients was studied. Angles were measured between the PN axis and the nearest PB (α), the furthest PB (β), and between the two PB (γ). On day 2, the morphological grades of embryos were recorded. γ ranged from 0 to 150° and was not significantly different for ICSI or IVF embryos of different grades; however, an unusual distribution of γ suggested different populations of oocytes. The first hypothesis was rejected. α and β ranged from 0 to 90°: α did not relate significantly to embryo grade, but β increased significantly with decreasing quality of ICSI embryos (P < 0.05) and the total group (P < 0.01), supporting hypothesis (ii). The difference in β between ICSI and IVF embryos was not significant, so hypothesis (iii) was unproven. Significant differences between ICSI and IVF embryos in PN positions, irregular cleavage, and cleavage failure were noted.