Green’s Dictionary of Slang

a woman’s swollen stomach, indicating her pregnancy; thus the embryo itself .

c.1564		Buggbears in R.W. Bond Early Plays from Italian (1911) III ii: Her greatest disease ys a spice of the timpanye.
1608		Dekker Ravens Almanacke in Works IV 217: Before three monethes were past [...] they had a spice of Timpany.
1608		Pennyless Parliament of Thread-bare Poets 11: Some shall have a Tymphany in their Bellies.
1612		W. Fennor Cornu-copiæ 17: If that they chance a countrey maid to pricke, And with a Timpanie the wench grows sicke, Then straight his seruing-man ... Must be a couer to his maisters stoole.
1632		J. Shirley Love in a Maze IV iii: If she be troubled with a tympany, there is a man within a mile of an oak, I name nobody, that has had – some earnest of her body.
1640		J. Gough Strange Discovery II v: ‘How comes your belly so high?’ ‘’Tis nothing but a timpany I am sometimes troubled with.’.
1663		Dryden Wild Gallant V ii: A mere tympany, sir, raised by a cushion.
1673		M. Stevenson Norfolk Drollery 84: The Earth’s deliver’d of a Timpanie, / And all the Captives of her womb set free.