Board Thread:Manga/@comment-30064439-20161113032209/@comment-33637057-20180710022318

Eren being aware of Historia's pregnancy all depends on how far along she is and how long Eren was gone from Paradis. I think it's safe to say that he was gone at least 3 months. Historia looks very late in her pregnancy (I'd estimate she's over 7 months along) but appearences can be deceiving so it's hard to tell. That being said, I wouldn't be surprised if the spark that made Eren go rogue was him hearing about her being pregnant.