Okay, I was just impatient. You need to also wait for Miko to be further into her pregnancy.
Might not be related but when I talked to her about her pregnancy, I got a converstation about her trying to tempt the champ' and the latter admonishing her for indulging in her gluttony. Might be an indicator on how far along she is, since the threesome option was unlocked on the same day I got the convo.