Green’s Dictionary of Slang

to become pregnant.

1936		N. Coward Tonight at 8.30 142: A couple of months later you’d told me you’d clicked, you cried a hell of a lot, I remember .
1954		Landfall VIII 228: In Wellington, just before he came down there was Heather, who had ‘clicked for a baby’ .
1982		P. Bailey Eng. Madam 45: I had sex with Terry and I clicked. [Ibid.] 56: He found a couple who couldn’t click and they took him.