A mature oocyte, described in the laboratory as MII, has completed the stage of development needed for fertilisation and is the type of egg used for ICSI or IVF insemination. Eggs found at earlier stages, MI (metaphase I) or GV (germinal vesicle), are described as immature and generally cannot be fertilised on the day of collection. Not every egg collected at egg retrieval is mature; the proportion varies between people and between cycles for the same person. Some immature eggs mature briefly in the laboratory dish before use, but this is not guaranteed, and immature eggs are not a reflection of a person's overall fertility.
Also known as: MII, mature egg, MI, germinal vesicle, GV, immature oocyte, immature egg
Related India guides
Sources
- ICMR Standard Treatment Workflows (icmr.gov.in/standard-treatment-workflows-stws)
- European Society of Human Reproduction and Embryology (eshre.eu)
Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.