Regency romance: pregnant heroine lies about whereabouts in order to nap, husband suspects affair

I thought this might have been The Dutiful Rake by Elizabeth Rolls, but I recently reread it and nope. Maybe Allison Lane, or a similar author?

Basic plot: main characters are married and possibly trying to ride out/downplay some scandal, so it's important for the wife to attend society functions and not decline invitations from important people. But she's newly pregnant and tires easily so she uses subterfuge to sneak afternoon naps. She tells Hostess A she can't make it because she already promised to attend Hostess B's party, etc., and really just stays home.

It comes to a head when the husband tries to find her one day, and everywhere he goes someone tells him she's somewhere else. He thinks she must be hiding an affair, but an older lady (possibly a relative) has figured it out and sets him straight. He immediately packs up his wife to their country house so she can rest and recuperate. Anyone recognize it?

Edit: Solved! The Reasons for Marriage by Stephanie Laurens