How to get OrganizationRelationships with a webhook?

I am trying to integrate Pipedrive into our ERP solution. At the moment I have been successful at updating Organizations into our system with webhooks. However, I need to recreate the Organization hierarchy as well, but I am not getting any information about related Organizations from webhooks (tried * . *).

I know I can use the /organizationRelationships API to get the relations, but I get no webhook notification when the relations change. Do I really have to poll for the relations data???