How did you tell your own parents?

I (35) recently made the choice to move forward with being a SMBC, I’m in the process of starting my IUI and have a donor! I’ve talked with one close friend but am looking for advice of telling your own parents about your decision. I know that they will be happy to have a grandchild but I don’t even know if the IUI will work, did you wait until you were pregnant or did you tell them before. I think my parents will be surprised but supportive I just have no idea how to broach the subject. Any advice or support is appreciated!