"I am sure we can find out."

He doesn't remember exactly when you can tell, but he thinks it's by now.

And even if under normal circumstances medicine can't... they hang out with a lot of telepaths, and the Mansion's infirmary has a whole lot of variously advanced technology.

Anyway, he doesn't object to knowing. Piotr sees no particular appeal in this mystery, and knowing helps with logistics like, say, picking names.