Is it permissible to inform one's employer about the nature of a health problem (fertility treatment) to justify frequent absences, especially with the possibility of undergoing an IVF procedure and the need for rest afterward?

There is no harm in disclosing the reason for frequent leaves to the manager, provided that Islamic guidelines concerning speech, hijab (definition), gaze, and avoiding seclusion and anything that raises suspicion are adhered to. The matter can also be written down and submitted in writing, along with attached copies of leave requests and hospital appointments.