Fertilization and early embryology: The chromosomal complements of multipronuclear human zygotes resulting from intracytoplasmic sperm injection

Abstract

Implementation of intracytoplasmic sperm injection (ICSI)in human in-vitro fertilization (IVF) has highlighted the need for information about the risk of nuclear spindle damage caused by this procedure. For this purpose we studied the final products of oocyte meiosis at the first cleavage division of multipronuclear zygotes arising after ICSI, and compared the results with abnormally fertilized oocytes after conventional in-vitro insemination. Of 37 successfully analysed tripronuclear zygotes, 18 had three individual metaphases. Abnormal complements of 11 zygotes in this group indicated that non-disjunction occurred predominantly at the second meiotic division of the oocytes. Nine of the 37 tripronuclear zygotes exhibited two individual metaphases. Seven were abnormal and there were some indications that non-disjunction took place during oocyte meiosis. Of the 37 tripronuclear zygotes, 10 had a single metaphase and three showed an aneuploid number of chromosomes. The overall rate of aneuploidy among tripronuclear microinjected zygotes was 56.7%. In addition, seven zygotes with more than three pronuclei arising after ICSI displayed severely depleted chromosome complements. The incidence of non-disjunction in oocytes fertilized by conventional in-vitro insemination was significantly lower (20.0%, P < 0.01), since only four zygotes had an aneuploid number of chromosomes. Our findings suggest that ICSI might interfere with regular chromosome segregation at the second meiotic division of the oocytes.

Origin of tripronucleate zygotes after intracytoplasmic sperm injection

“…This phenomenon could arise from the abnormal distribution of the maternal chromosomes into two separate sets after extrusion of the first PB. Moreover, the incidence of this abnormality could be increased by the hydrostatic pressure exerted during the ICSI procedure, thus disrupting the microtubules of the oocyte spindle, as previously suggested by Macas et al (1996), who reported a 32% incidence of diploid embryos erroneously classified as 3PN, although their results were based on cytogenetic studies. Oppositely, our rate of 36% of diploid embryos does not agree with the rate of 13.2% recently reported by Staessen and Van Steirteghem (1997), after FISH studies of cleaving embryos from 3PN, ICSI-derived zygotes.…”

“…Van Steirteghem et al (1993b) and Nagy et al (1995) reported percentages of 5.1 and 2.4 respectively, and more recently Macas et al (1996) and Staessen and Van Steirteghem (1997) reported rates of 6.2 and 6.5% respectively. These data are similar to the incidence reported by the two IVF laboratories involved in this study, 3.9% (J.M.Calafell, personal communication) and 3.3% (GilSalom et al, 1996).…”

“…However, in some circumstances, observation of the PB can be difficult, and the possibility of PB degeneration after 2762 © European Society for Human Reproduction and Embryology several h of in-vitro culture cannot be discarded. Moreover, the morphological evaluation of the zygotes can lead to misinterpretation of the ploidy when supernumerary micropronuclei are observed (Macas et al, 1996).…”

Effect of sperm entry on blastocyst development after in vitro fertilization and intracytoplasmic sperm injection — mouse model

“…Some studies suggest that the ICSI technique might disturb regular chromosome segregation at the second meiotic division of the oocytes [27]. Typically, the sperm injection during ICSI is performed away from the PB1, regularly used as a marker of chromosomes in the metaphase II oocytes [3].…”

“…Despite documented efficiency and success in infertility treatment using ART, there is increasing evidence of congenital malformations and chromosome aberrations in children born after ICSI and IVF [14,15,20,29]. A study that assessed the risk of nuclear spindle damage following ICSI suggests that this technique might interfere with regular chromosome segregation at the second meiotic division of the oocytes [27]. It is possible that ICSI affects an important event(s) that occurs in the narrow time-window between fertilization and pronucleus formation, thus affecting the long-term cascade of gene expression and embryonic development [12,18,25,32].…”