Ranma started to say something, but then closed his mouth, and looked
around. 'Hmm,' he thought. 'Probably not the best of things to be talking
about in a public street.' He gestured Nodoka inside. "Perhaps you'd
better ask HER that. I'm not entirely sure she would want me to discuss
this sort of thing out here." Nodoka's eyes became slivers.
These are the things that Ranma is justly famous for. His tact, his
discretion, his ability to think before speaking, his etiquette, and
his care to eschew colloquialism in favour of formal speech. Not.
Might I suggest instead that he take one of two alternatives? Either
he treats it casually and says something to the effect of
"Natsume got herself knocked up, so Mr. Tendo invited her to stay until
after she pops.", or he gets embarassed about talking about something like
that to his mother, starts to stutter and says, "Maybe you ought to ask her."