Fertilization abnormalities and pronucleus size asynchrony after intracytoplasmic sperm injection are related to oocyte postmaturity.
OBJECTIVE
To study the effect of delayed intracytoplasmic sperm injection (ICSI) on the fertilization and cleavage of human in vitro matured (IVM) oocytes.


METHODS
Prospective experimental study.


METHODS
Academic hospital-based fertility center.


METHODS
The experimental group consisted of 73 spare germinal vesicle-stage oocytes from 25 patients. The control group consisted of sibling in vivo matured oocytes from the same patients that were subjected to ICSI in the clinical program.


METHODS
Equal numbers of sibling IVM oocytes were subjected to ICSI either soon after maturation (30 hours, group 1) or after a 6-hour delay (36 hours, group 2). In a subsequent set of experiments, spermatozoa were labeled with a fluorescent mitochondria-specific vital dye and injected into 17 IVM oocytes that were intentionally aged by 6-8 hours. The resultant zygotes were fixed.


METHODS
Incidence of fertilization and cleavage, numbers and mean diameters of pronuclei, and incidence of zygotes with significant pronucleus size asynchrony. Identification of the male pronucleus by its proximity to the fluorescent sperm midpiece remnant.


RESULTS
Group 2 had significantly lower rates of normal fertilization (60%) than the control group (82.9%) and significantly lower cleavage rates (46.7%) than both group 1 (85%) and the control group (98.1%). The incidence of oocytes that developed one pronucleus and pronucleus size asynchrony was significantly higher in group 2 (32% and 40%, respectively) than in group 1 (4% and 5%, respectively) and in the control group (4.1% and 4.4%, respectively). All the zygotes with significant pronucleus size asynchrony that developed after delayed ICSI with labeled spermatozoa showed proximity of the fluorescent sperm midpiece remnant to the smaller pronucleus.


CONCLUSIONS
For IVM oocytes, the incidence of one pronucleus, pronucleus size asynchrony (possibly related to a smaller male pronucleus), and cleavage failure increase when ICSI is delayed after maturation. Thus, the timing of ICSI is critical for optimum fertilization of IVM oocytes.
Goud
P
P
Department of Obstetrics and Gynecology, University Hospital, Ghent, Belgium. pravin.goud@rug.ac.be
Goud
A
A
Van Oostveldt
P
P
Van der Elst
J
J
Dhont
M
M
D002467:Cell Nucleus / Q000648:ultrastructure; D003593:Cytoplasm; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D008297:Male; D008677:Metaphase; D008928:Mitochondria / Q000648:ultrastructure; D009865:Oocytes / Q000166:cytology*; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000166:cytology* / Q000502:physiology*; D015053:Zygote / Q000166:cytology* / Q000502:physiology*