Germinal vesicle breakdown (GVB) refers to the dissolution of the nucleus of an oocyte that is arrested in prophase of meiosis I (the breakdown of the germinal vesicle). In this stage, the oocyte resumes meiosis in response to the luteinizing hormone (LH) surge that occurs prior to ovulation. The oocyte will arrest in meiosis II at the metaphase (MII) stage, where it stays until fertilized by sperm.