The answer is something the late Tywin Lannister would be proud of - Cersei has realized that she needs to meet with Daenerys Targaryen. not to align together in the face of an even graver threat as the Night's King and his army of the dead march into Westeros, but in order to win a war she can not win on the battlefield.
At face value, the fact that Cersei is evidently pregnant again proves Maggie's prophecy wrong. Given the option I would much rather have her express her cunning by manipulating Jaime with a false preggers storyline, than putting forth another example of how women have no motivation without our precious womb, but I guess both options are regressive, and it does seem fair that she's already watched three of her kids croak. And, while Gilly doesn't exactly know the heavy importance of this information she gleaned from an old maester's records yet, we definitely do. Basically, it should be clear to HBO that this is a bad time to discuss a show like this, but the people involved with Confederate have once again chose to stick to their guns instead of surrendering to common sense. Pair that with a few days away with Bronn (who is King of Not Giving A Fuck) and we may have a very flakey brother-lover on our hands.
But what about that chat with Qyburn? "He's shocked, of course, but he believes her because I think, when you look at Cersei, she actually seems surprisingly happy", said Coster-Waldau. Meaning that Cersei could die in childbirth, thereby fulfilling the prophecy. Jaime walks in while Cersei is consulting with Qyburn.
How does Cersei's pregnancy fit in with the prophecy?
We surely weren't the only ones thinking it.
Now, remember back in season five when we saw Maggy the Frog, a fortune-telling witch unfortunate dematologic issues, creepily predict young Cersei's future? Maggy the Frog says that Cersei will marry the king, not the prince; that another younger, more attractive queen will take all that is dear to Cersei; and that Cersei will bear three children, all of whom will die - "gold will be their crowns, gold their shrouds". "Gold shall be their crowns and gold their shrouds".More news: Taiwan concerned by U.S. plan for unfair trade probe against China
More news: Marriage vote to occur before year's end
More news: Sharapova (forearm) withdraws from Stanford tourney
Also, the prophecy that Cersei got from the woods witch said her only three children would die, and now they have. There was no mention of a rogue fourth baby. Seriously, what did he think was going to happen?
Children born of incest are way more likely to have some medical issues, babies born of incest and who are a direct descendant of Cersei Lannister are nearly guaranteed to be absolute fruitloops. We know that Sam was effectively stripped of his birth right by being sent to the wall.
The pair have a lot of similarities, and a truly mad theorist could go as far to say that Bran and The Night King are one and the same. She had her interest in swords, arrows and crossbows.
She knows she's losing the war, and will do anything to gain an advantage. However, Jaime is also her little brother as Cersei is the elder twin. Technically, he is then still responsible for her death.
This speculation isn't entirely baseless - there was a brief, nearly offhand mention to a potential problem in the most recent episode of the show, Eastwatch, which may prove to be the start of a schism that drives Jon and Daenerys apart.