In vitro blastocyst formation of human oocytes obtained from unstimulated and stimulated cycles after vitrification at various maturational stages.

OBJECTIVE To evaluate the developmental competence and chromosomal normality of oocytes vitrified at various times after maturation culture. DESIGN In vitro model study. SETTING A university-affiliated hospital. PATIENT(S) Unstimulated women who underwent cesarean section or oophorectomy and infertile women who underwent a long protocol of GnRH stimulation. INTERVENTION(S) Retrieved oocytes were vitrified at 0 or 48 hours after culture in unstimulated cycles and at 0, 8-15, or 24-28 hours after culture in stimulated cycles. MAIN OUTCOME MEASURE(S) Postthaw morphologic normality, maturation, fertilization, cleavage, blastocyst formation, and chromosome number. RESULT(S) In the 53 oocytes that were obtained from unstimulated cycles, no statistically significant differences were found in rates of morphologic normality (range, 56%-63%) or fertilization (range, 31%-37%) according to the time of vitrification. In the 50 oocytes that were obtained from stimulated cycles, more of those that were vitrified at 24-28 hours were morphologically normal than those that were vitrified at 0 or 8-15 hours. Regardless of these differences, high cleavage rates (83%-100%) were obtained that did not differ significantly among the treatment groups. In both cycles, 20%-43% of cleaved oocytes developed to the blastocyst stage by 6 days after IVF. All the karyotyped blastocysts, three from unstimulated cycles and four from stimulated cycles, had a normal number of chromosomes. CONCLUSION(S) Vitrified and thawed oocytes from unstimulated or stimulated cycles developed to the blastocyst stage, regardless of when vitrification occurred; the number of chromosomes in the blastocysts was normal.