The parent cells that produce oocytes are called oogonia. Oogonia are diploid cells. All the oogonia start, the process of meiosis and form primary oocytes prior to birth. They are arrested in prophase I and remain this way until the female reaches puberty, until a preovulatory surge of luteinizing hormone (LH) from the pituitary stimulates meiotic resumption. The prophase I-arrested oocyte acquires the ability to resume meiosis as it approaches its full size.