Kate almost rolls her eyes for that, but she realizes Magnus really isn't used to trusting her with personal stuff, and she doesn't take it personally. Magnus isn't really used to trusting anyone. So Kate keeps the eye roll to a Look, quirks a grin, and says, "Holy shit, you're pregnant? Congratulations!" like this is first she's heard of it.

"In case you need a translation, that's, this is your baby, your story. I don't know anything until you tell me I do."