The zona pellucida (ZP) may vary in thickness and rigidity. Some patients have clearly thinner ZP than others. It is usually a characteristic associated with the patient more than with the oocyte. Although thickness may vary slightly around the oocyte, the following categories can be defined.
|Thin||the ZP is less than 15 µm|
|Thick||the ZP is greater or equal to 25 µm|
|Normal||the ZP is around 20 µm (15-25)|
|Abnormal||the ZP is quite irregular both in thickness and in shape|