User blog comment:HowtobeaGrimm/Juliette's Pregnancy/@comment-3125844-20151001172046/@comment-26976525-20151001201224

I didn't say that Nick knew she was pregnant. I think only Rosalee guessed that from Juliette's symptoms.

It's knowledge that Rosalee will later use to hurt Nick, when Nick attacks Monroe or Trubel or some else. If Nick gets out of control with his blaming others, Rosalee will throw that back at him and cut him to the quick.