In most animals, oocytes are held in meiotic arrest in prophase I prior to ovulation. The ovulatory luteinizing hormone (LH) surge promotes the resumption of meiosis of the arrested oocytes and their progression through the second meiotic cycle, only to be arrested again at metaphase II until fertilization.

At which stage oocyte is arrested?

The Regulation Mechanism of Oocyte Meiosis Arrest at Prophase I. Before an oocyte is enclosed by ovarian granulosa cells to form primordial follicles, meiosis has been initiated and the cell has arrested at the diplotene stage of prophase I (Bowles et al., 2006; Bowles and Koopman, 2007).

Why oocyte is arrested at metaphase?

Oocytes from higher chordates, including man and nearly all mammals, arrest at metaphase of the second meiotic division before fertilization. ... Cytostatic Factor maintains arrest through preventing loss in Maturation-Promoting Factor (MPF; CDK1/cyclin B).