Green’s Dictionary of Slang

to become pregnant.

1959		D. Hewett Bobbin Up (1961) 24: Thank Christ I’m too old to fall.
1962		C. Rohan Delinquents 150: Who would think I’d be so stiff as to fall again?
1967		N. Dunn Poor Cow 78: Do you know you can fall with a white man and have it with a coloured bloke when you’e carrying and it’ll turn out a half-caste?
1970		H.E. Bates A Little of What You Fancy (1985) 581: He didn’t think they fell nowadays, what with the Pill and all that.
1981		J. Sullivan ‘Big Brother’ Only Fools and Horses [TV script] Do you know she was 39 when she fell for you?
1989		J. Morton Lowspeak.