Record scratch: let's head all the way back to Book 1, Chapter 21, when Mr. Shandy took his pipe out to wonder what the racket upstairs was. Obadiah, the servant, clears things up: baby Tristram is on his way, and Mrs. Shandy's servant Susannah has run off to fetch the midwife.
Mr. Shandy orders Obadiah to leave immediately to fetch Dr. Slop. He can't figure out why Mrs. Shandy would bother sending for the midwife, since Dr. Slop is so close. Toby suggests that Mrs. Shandy might be modest: maybe she doesn't want a man so near her ---
Conveniently, Mr. Shandy's pipe snaps before Toby has to finish his sentence.