So i had this problem when trying for baby that I would not hear the lullaby even when the sim ended up pregnant..but I tried different things and I had "Replace Woohoo with Risky Woohoo" on but then i turned the option off - and now I could hear the lullaby. Why does having that option on mute the lullaby for me? I want to keep the option on. I do have lots of mods

I don't have a fix but wanted to say I've seen the same thing, and I've mentioned it to other people who are wondering what the lullaby went and that was the cause for them too. Perhaps it's by design—maybe people don't want to know whether the Risky Woohoo "worked" or not, at least not right away.

I play with the pregnancy sting removed in all contexts, but yes I think it's intentional that the audio cue would give away what Risky rolled.

You can use MasterController as somewhat of a player-side pregnancy test, by accessing it from that Sim and checking Status > Relationship, if confirmation is the only reason you want to keep the audio. If a pregnancy is active, information about it will be listed there.