Aberrant DNA methylation of imprinted loci in human in vitro matured oocytes after long agonist stimulation.

To evaluate the epigenetic risk linked to assisted reproductive technology at oocyte level by analyzing methylation status of imprinted H19, PEG1 and KvDMR1 in human MII oocytes rescue-matured from MI/GV oocytes after long agonist stimulation.580 MI/GV oocytes from 275 patients receiving an ICSI procedure were additionally cultured for 24h, and 221 rescue-matured MII oocytes were obtained. Pyrosequencing with confirmatory routine bisulfite sequencing were used to determine the methylation status of H19 DMR in 35 oocytes, PEG1 DMR in 47 oocytes, and KvDMR1 in 34 oocytes.Abnormal methylation status were found in 22.9% oocytes at H19 DMR, 17.0% oocytes at PEG1 DMR and 8.8% oocytes at KvDMR1.We hypothesize that the use of MII-rescue oocytes may increase the risk of imprinting defects because they might not have completed full imprinting programme.