metaphase I oocyte
Also written as: MI
Immature egg cell arrested in the first meiotic division, requiring maturation before fertilization.
Full Definition
A metaphase I (MI) oocyte is an immature egg cell that has not completed its first meiotic division and lacks a visible polar body. These oocytes are characterized by the presence of a germinal vesicle that has broken down but meiosis I has not been completed, with chromosomes arranged at the metaphase plate. MI oocytes cannot be fertilized using conventional IVF or ICSI until they complete maturation to metaphase II. In laboratory practice, MI oocytes may undergo in vitro maturation over 24-48 hours, though the resulting embryos typically have lower developmental potential compared to those from naturally mature oocytes.
Usage
Usage note: Requires completion of meiosis I before fertilization attempts
In Context
- "Three metaphase I oocytes were placed in maturation culture medium." — Laboratory protocol
- "The retrieval yielded 8 mature and 4 metaphase I oocytes requiring further maturation." — Embryology report