Date of Award
Doctor of Philosophy (PhD)
R. James Swanson
Despite adequate hormonal stimulation, oocytes collected for the purpose of in vitro fertilization and embryo transfer display several levels of nuclear maturity. Preovulatory or mature oocytes, technically those that are Metaphase I or II, are inseminated shortly after aspiration and assessed for fertilization the following day. Prophase I oocytes, also called germinal vesicle-bearing or immature oocytes, require a 24-36 hour period in culture before being exposed to spermatozoa. During this time, the majority of Prophase I oocytes complete nuclear maturation in vitro, progressing from germinal vesicle breakdown through first polar body extrusion. If inseminated, many in vitro matured oocytes fertilize and appear to develop normally. However, compared to embryos derived from mature oocytes, embryos derived from Prophase I oocytes produce significantly fewer pregnancies following intrauterine transfer. To determine if the reduced developmental potential of embryos derived from Prophase I oocytes can be explained in part by an increase in nuclear and/or genetic abnormalities, this study used Fluorescence In Situ Hybridization analysis to compare 65 embryos derived from oocytes that were Metaphase I or II at aspiration to 61 embryos derived from oocytes that were Prophase I at aspiration. Although there was no difference in the incidence of multinucleated blastomeres in the two groups, embryos derived from Prophase I oocytes had a significantly higher incidence of both anuclear blastomeres and blastomeres with a fragmented nucleus compared to their counterparts derived from mature oocytes. Because nuclear fragmentation is a hallmark of programmed cell death and subsequent apoptosis, which has been implicated in the processes of follicular atresia in vivo and cleavage arrest in vitro, we speculate that Prophase I oocytes obtained following controlled ovarian hyperstimulation originate from follicles in early stages of atresia. This study found no difference in the rate of aneuploidy for chromosomes X, Y, and 18, or in the incidence of mosaicism involving these chromosomes in the two groups of embryos. However, according to our classification system, 23% of embryos derived from Metaphase I or II oocytes were normal compared to only 3% of embryos derived from Prophase I oocytes. Our findings suggest that few embryos derived from Prophase I oocytes are normal, perhaps explaining in part why they rarely establish pregnancies in our IVF program.
"Fluorescence in Situ Hybridization Analysis of Human Embryos Derived From in Vitro and in Vivo Matured Oocytes"
(1997). Doctor of Philosophy (PhD), dissertation, , Old Dominion University, DOI: 10.25777/769q-8w14