i had a dermoid cyst on my right ovary, found during pregnancy through u/s. had had considerable abdominal pain for about 3 yrs which went undiagnosed after ongoing tests. the cyst was removed during emergency c/s and was sent for testing, it was benign and ob advised they rarely are cancerous, rarely affect ttc, but can cause pain, in some cases they dont cause pain, but usually do. she said it was nothing to be concerned about but if they are left for long periods of time they have a higher risk of becoming cancerous and are better off removed. it did stop the pain for about 6 months, then the pain returned at which point u/s was done to see if it had returned but it hadn't. pain has now gone again.

i hope everything goes well for your sil