Embryology
The zona pellucida is a protective outer shell made of proteins that surrounds an egg and continues to surround the embryo in its earliest days of development. Sperm must interact with the zona pellucida to fertilise an egg, and the embryo must later break out of it, a process called hatching, in order to be able to implant in the uterine lining. The zona pellucida's thickness and appearance can be relevant to techniques such as ICSI, embryo biopsy and assisted hatching, all of which involve deliberately creating an opening in it under laboratory conditions.
Also known as: zona
Sources
- ICMR Standard Treatment Workflows (icmr.gov.in/standard-treatment-workflows-stws)
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.