The usefulness of metaphase I oocytes in women who undergo controlled ovarian hyperstimulation for intracytoplasmic sperm injection.

OBJECTIVE The aim of this study was to evaluate the fertilization and blastocyst formation rates of oocytes in metaphase I (MI) obtained from women who underwent controlled ovarian hyperstimulation (COH) for intracytoplasmic injection. METHODS A prospective cohort study that included women from whom at least 1 MI and 1 MII oocyte were obtained after COH was performed. We collected 1,907 oocytes from 164 women (1291 MII, 352 MI and 258 prophase I or atretic). After oocyte classification, the MII and MI oocytes were incubated for 4 hours. RESULTS After 4 hours, the rescue maturation rate was 57.2%; 205 MI oocytes matured to MII oocytes in vitro (rescued MI-MII group), and 153 remained in MI (arrested MI group). The normal fertilization rates were directly associated with oocyte maturation, with rates of 79.1%, 60.2%, and 31.9% in MII, MI-MII and MI oocytes, respectively (p<0.001). Group arrested MI had an odds ratio (OR) of 7.6 (CI 5.2 - 11.2, p<0.001) for abnormal fertilization compared with Group MII. The blastocyst formation rate was directly associated with oocyte maturation, at 36.4% for MII, 11.4% for MI-MII and 0.6% for MI. CONCLUSION Oocytes collected at the MI stage after OCH that did not mature to MII after rescue maturation had a blastocyst formation rate of only 0.6%, while those in MII and MI-MII had rates of 36.4% and 11.4%, respectively. However, we found a pregnancy with the birth of a healthy baby from a blastocyst formed after intracytoplasmic sperm injection (ICSI) of an MI oocyte.