Heya and welcome to the forum
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I’m afraid this is not a bug, but not implemented yet to have a 100% contraception option. Here is a post that already mentioned that issue, if you want to check it:
I do agree that there should be an option that 100% prevents pregnancy. Especially if a person wants to play a Zoi, that wants to lead casual relationships or just don’t want a child yet.
The “asking for baby”, as far as I understand has a higher or even 100% chance to get pregnant while “set the mood” has the risk.