Dear Member,
In case you were covered under ESI Act, then you should have got necessary certification before start of maternity leave from your authorised ESI Dispensary.
Now, at this stage, you can consult Insurance Medical Officer of your ESI Dispensary as well as Branch Manager, of appropriate Branch Office of ESIC to which you are attached and discuss the matter with them.
I hope, keeping in view your eligibility from records as well as certificate from private hospital from where you obtained the treatment during maternity leave, the above offices will guide you as may be permissible with rules/regulations at this stage.