It is not Goldsmith using the word "pregnancy," it is one of his characters. A big difference, I think.

In Pride and Prejudice, it is the clergyman, William Collins, who writes of his wife's pregnancy. THAT is a word that Mr. Collins would never use: it would be completely out of character! He thinks himself so perceptive in the 'delicate ways' of females. He would, of course, use euphemisms for pregnancy because he would consider the situation too personal (touching, as it does, upon sexual relations) to approach openly with ANYONE, including his wife!