Vitrification at the germinal vesicle stage does not affect the methylation profile of H19 and KCNQ1OT1 imprinting centers in human oocytes subsequently matured in vitro

Objective: To evaluate the integrity of genomic imprinting in oocytes vitrified at the germinal vesicle (GV) stage and in vitro matured (IVM) after thawing. Design: Clinical research and application. Setting: University-based fertility center. Patient(s): Immature oocytes were donated for research by patients who were included in an intracytoplasmic sperm injection program. Intervention(s): Immature oocyte retrieval after ovarian stimulation, followed by oocyte vitrification, thawing, and IVM. Main Outcome Measure(s): Methylation profile of H19 and KCNQ1OT1 imprinting control regions, H19DMR and KvDMR1, respectively. Result(s): Among 184 vitrified GV oocytes, 102 survived thawing (55.4%), 77 (75.5%) of which reached the meiosis II (MII) stage after IVM. One hundred twenty control GV oocytes were only subjected to IVM; 70.8% reached the MII stage. GV vitrified as well as control oocytes acquired full imprint at KvDMR1 after IVM and generally retained the unmethylated state of H19DMR. Conclusion(s): For the first time, we show that oocyte vitrification does not affect the methylation profile of H19DMR and KvDMR1: during their IVM, vitrified GV oocytes acquire DNA methylation in the maternally imprinted KCNQ1OT1 gene with the same efficiency as fresh GV oocytes; the vitrification process does not alter the unmethylated state of the paternally imprinted H19 gene. (Fertil Steril (R) 2011; 95: 1955-60. (C)2011 by American Society for Reproductive Medicine.)