blighted ovum for the third time

Hi!
I am having a blighted ovum for the third time now. I had one in my first pregnancy after that i had a good pregnancy with a healthy child. after that I had another blighted ovum and after that healthy pregnancy again. and now I have another blighted ovum for the third time!
what can be the cause of it? do i need to ask for testing at this point?
can my eggs be too old?