Maternity leave and performance appraisal are two unrelated things. These need not be linked. However, we need to know about your company's performance cycle. What is the duration of your performance cycle? Who will do your Performance Appraisal (PA), when will it be done and how will it be done? Who designed your KRAs and do you have evidence of the attainment of the KRAs? Who told you that there will not be PA for you? Have you read the Policy on PA? Does it include clause on exclusion of woman employees who are due to proceed on maternity leave?
We do not know about your company's policy on performance appraisal. However, application of any policy is always uniform. Therefore, you might have to put up application for conducting the PA for you. You may proceed on maternity leave as scheduled however, maintaining records about PA in your personal file are important. Not having PA records might create adverse repercussion for you. Who knows some gentleman in future might construe it as your zero performance. You need to foreclose this eventuality now itself.
For further queries, feel free to contact me.