[Main Spoilers] Cersei's revelation - does it affect a popular theory?

So...Cersei's pregnancy announcement.... How does it affect the theory that Jaime is the valonquar and is going to kill her? As much as Jaime's character is a shade of grey, I don't think he'd ever kill his child no matter how insane Cersei became. So...is it commonly viewed on here that she's lying? Just like a psycho high school girlfriend? Might the fact she's lying be one of the reasons Jaime snaps and kills her?