I mean yan an really doesn't want children anyway which she has already expressed by choking ruo yun that time, so she is probably thinking this is killing 2 birds with 1 stone. She can save him and render him infertile. Dunno if she is that cruel but we will see.
@Cookie90, its not that she doesn't want children, there's a reason she's taking the contraceptive soup instead of making him take it. Also I think the reason she said that to ruo yun was because he wanted to manipulate her into favoring him, so his family could get power.
I know yan an is doing this for a reason...but it still makes me so angry to see fei yue treated like this. Yeesh, why do bad things keep happening to him? He doesn't deserve it..