I have a donor egg conceived daughter. It wasn’t something I chose to do lightly and my main concern was if it would/could affect her negatively in later life. After a lot of consideration, conversations with psychologist and reading into it, I came to the conclusion that as long as we were upfront about her origins from the get go then it should cause no psychological damage to her in the future. My experience with adopted children in my wider family also reassured me about this.
Before pregnancy I only told a close friend, my husband told no one. Once pregnant I told my sister. I don’t think it would’ve been that much of a shock that I was pregnant through IVF at least. I told my parents about a month or so after she was born.
Egg donation is quite a different thing to do and people can struggle to get their heads round it (5 years ago I wouldn’t have considered it). This is why I held off telling most people until after she was born. By that point they’d bonded and they already loved her as their own. I don’t think they would love her any less if they had found out during pregnancy - my sister certainly couldn’t love her more and she feels every bit her niece. But I didn’t want to give myself or them the extra stress. You can completely overthink these things when they are theoretical or the baby isn’t actually here yet, but the reality is once your baby is here it will feel completely normal, she/he will be completely yours and by extension completely their grandchild/niece/cousin.
I had concerns about how my parents would feel as on paper they wouldn’t be pro IVF and certainly not pro egg/sperm donation. I don’t suspect their views will really have changed even now, but that’s the funny thing about people, it’s never black and white - they can make exceptions, they can have a generalised stance but still be ok when something doesn’t go along with that stance. My daughter couldn’t be more loved by them and her story is what it is. They wouldn’t change her for the world.
So my advice would be tell someone through pregnancy so you have some support, someone to offload to. It’s also helps normalise the conversation. It’s been easier with every extra person I tell. I stressed about it before hand but it was always fine. For me it was right to tell parents after she was born. If it causes you more stress to keep a “big secret” then tell them now - go with your gut and it will work out, you know the personalities and dynamics!