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 (alpha), the furthest PB (beta), and between the two PB (gamma). On day 2, the morphological grades of embryos were recorded. gamma ranged from 0 to 150 degrees and was not significantly different for ICSI or IVF embryos of different grades; however, an unusual distribution of gamma suggested different populations of oocytes. The first hypothesis was rejected. alpha and beta ranged from 0 to 90 degrees : alpha did not relate significantly to embryo grade, but beta increased significantly with decreasing quality of ICSI embryos (P < 0.05) and the total group (P < 0.01), supporting hypothesis (ii). The difference in beta 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.

The combination of pronuclear and blastocyst morphology: a strong prognostic tool for implantation potential

“…In our study, we noted that the PN size may influence the TE morphology, but neither the PN size nor its orientation had any impact on any other blastocyst feature or on the clinical outcomes. Several authors have reported inconsistent results regarding the influence of PN orientation on embryo development and implantation [9][10][11]. According to Senn and colleagues [2], PN position is not correlated with successful implantation, but the NPB patterns are relevant indicators of implantation, which is in keeping with our findings.…”

“…However, several authors have reported different results regarding the prognostic value of each PN feature. Some studies have reported a strong association between the PN orientation [9][10][11] or the number and distribution of NPB [12][13][14][15][16] and the implantation potential; others have suggested that an increased chance of implantation exists when the cytoplasmic halo is present in zygotes [2,[17][18][19][20][21].…”

Oocyte euploidy, pronuclear zygote morphology and embryo chromosomal complement

“…In light of these considerations, it is not surprising that a correlation exists between pronuclear zygote morphology and embryo viability. The consequences of incorrect positioning of pronuclei could cause several effects such as the unequal distribution of mitochondria to blastomeres, incorrect positioning of centrosomes or not proper alignment of nuclei on the polar axis (Garello et al, 1999;Van Blerkom et al, 2000;Tesarik et al, 2002). In all cases, abnormal development will follow.…”

“…Nucleolar morphology was classified according to their position and size within the pronuclei: 1-large size and aligned; 2-large size, scattered; 3-large size, aligned in one pronucleus and scattered in the other; 4-small size, scattered and 5-any other configuration in which the two pronuclei totally differ between them. The position of polar bodies was described in relation to the longitudinal axis of pronuclei: α-in the longitudinal axis ±30°, β-perpendicular to the longitudinal axis ±30° and γ-in different angles with a rotation >30° off the longitudinal or the perpendicular axis (Garello et al, 1999;Scott, 2003). In Group 1, this evaluation was necessarily based only on the position of the second PB (PB2).…”

“…This condition could be a marker of developmental asynchrony between the two pronuclei, indicative of chromosomal abnormalities or altered meiotic events (Scott et al, 2000;Tesarik et al, 2000). Moreover, the evaluation of the angles subtended by pronuclei and polar bodies has suggested that wide angles might reflect a great degree of cytoplasmic turbulence with a consequent abnormal development (Garello et al, 1999).…”