Green’s Dictionary of Slang

tympany n.

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.

In derivatives

tympanize (v.)

to impregnate.

1618

Owles almanacke 25: [They] could finde in their hearts to hang themselues. In maides likewise that are tympanizde before their time, and in boyes that are sullen.

In phrases

be cured of a two-legged tympany (v.)

to give birth.

1685–88

‘The Innocent Country-Maid’s Delight’ in Ebsworth Roxburghe Ballads (1893) VII:1 28: When e’re they have been too free, / And happen with child to be, / The Doctor, be sure, is sent for to cure / This two-legged tympany.

two-legged tympany (n.) (also two-legged tumour, two-heeled tympany, tympany with two heels)

an unborn child, an embryo.

1590		Tarltons Newes 25: Timpany with two heeles.
1605		N. Breton I Pray You in Works II 8: [Ill luck to] fall into a two-heeld Tinpany.
1612		W. Fennor Cornu-copiæ 68: [...] a two legd Timpany.
a.1690		‘The Lass of Lyn’s Sorrowful Lamentation’ in Ebsworth Bagford Ballads (1878) I 463: Oh what will become of me, / My Belly’s as big as two; / ’Tis with a Two-legg’d Tympany, / I cannot tell what to do.
1770		D. Gunston (ed.) Jemmy Twitcher’s Jests 88: It fills our virgins heads with humours / And makes them swell with two-leg’d tumours.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1984		Partridge DSUE (8th edn) 1281/1: 1579–1850.