"Maybe this is just a mistake"-yui quickly grabbed a pregnancy test and did it again she waited for a while she was nervous and thought about what he would say. What if he make her abort the baby or if he leaves her.
Tsuna just wanted to see the reaction of the weirdos- I mean friends and family around him when he tells them that he is "pregnant". But things escalated quickly and went out of control... out of control as in worldwide out of control.