No it isn't
slang terms can mean different things to different groups of people, she lives in another part of the country, I heard somewhere that Northerners sometimes use different words for things. I'll try and find a citation for that.
(PsychoChomp, Tue 11 May 2010, 11:30, 2 replies, latest was 16 years ago)

We divven't, like.
It's southerners that use different words for things. You call lemonade 'beer' for instance.
( Davros' Granddad a voice of calm reason in a world of spastics., Tue 11 May 2010, 11:34, Reply)

Don't forget our invisible 'r's
barth
grarss
parth
( Naked Ape call me Caitlyn, Tue 11 May 2010, 11:36, Reply)

Well, quite.

( Davros' Granddad a voice of calm reason in a world of spastics., Tue 11 May 2010, 11:37, Reply)

So it should be in use in that context somewhere on the internet, then,
surely?

They do have the internet up north, don't they? Someone there would probably have added it to, say, urbandictionary.com, I would imagine.

www.urbandictionary.com/define.php?term=duffing%20up

3 definitions, none of which refers to pregnancy.
( Monty Boyce, My cheese game is strong, Tue 11 May 2010, 11:36, Reply)

No internet up North today, the coal delivery was delayed by an outbreak of poverty all over the M6

( Naked Ape call me Caitlyn, Tue 11 May 2010, 11:37, Reply)

Ugh. Repulsive.

( Monty Boyce, My cheese game is strong, Tue 11 May 2010, 11:37, Reply)

I'm here.
As is Gary. No break in service. Anyway, Monty's of fucking Scottish heritage, the patchwork skirt-wearing, ginger, heart attack waiting to happen.
( Davros' Granddad a voice of calm reason in a world of spastics., Tue 11 May 2010, 11:39, Reply)

You forgot alcoholic and servant of the English

( Naked Ape call me Caitlyn, Tue 11 May 2010, 11:39, Reply)

That too.
Monty's so servile he pretends to be one of them.
( Davros' Granddad a voice of calm reason in a world of spastics., Tue 11 May 2010, 11:40, Reply)

Worst teeth in Europe too.

( Monty Boyce, My cheese game is strong, Tue 11 May 2010, 11:41, Reply)

Shurrup ya mong!
I knows it cos we says it
( Roota zweeeeeoooooowm, Tue 11 May 2010, 11:39, Reply)

I think they mean this.
www.urbandictionary.com/define.php?term=up+the+duff
(Applebite Uh! A cow!, Tue 11 May 2010, 11:41, Reply)

So do I.

( Monty Boyce, My cheese game is strong, Tue 11 May 2010, 11:41, Reply)

me too
I agree with you

duffed up = beaten up
up the duff = pregnant

NO CROSSOVER!
( Vipros. clever got me this far, then tricky got me in, Tue 11 May 2010, 11:43, Reply)

There is round here
God shurrup the lorra yez.
Just because you find it impenetrable, doesn't mean we can't handle it.
( Roota zweeeeeoooooowm, Tue 11 May 2010, 11:45, Reply)

we all know you lot can't use the language properly

( Vipros. clever got me this far, then tricky got me in, Tue 11 May 2010, 11:46, Reply)

It's rich and varied
We'll do with it what we wish.
( Roota zweeeeeoooooowm, Tue 11 May 2010, 11:47, Reply)

what's it ever done to you?

( Vipros. clever got me this far, then tricky got me in, Tue 11 May 2010, 11:49, Reply)

I'm not abusing it
I'm merely using it
( Roota zweeeeeoooooowm, Tue 11 May 2010, 11:50, Reply)

there's a fine line between them
you and your kind have crossed that line.
( Vipros. clever got me this far, then tricky got me in, Tue 11 May 2010, 11:56, Reply)

Shut it
you goblin
( Roota zweeeeeoooooowm, Tue 11 May 2010, 12:04, Reply)

*gobbles*

( Vipros. clever got me this far, then tricky got me in, Tue 11 May 2010, 12:18, Reply)

She's not impenetrable, either.

( Davros' Granddad a voice of calm reason in a world of spastics., Tue 11 May 2010, 11:49, Reply)

GUV!!

( Roota zweeeeeoooooowm, Tue 11 May 2010, 11:50, Reply)

No
I've heard you can duff her up the duffer for 12 duffin' pence.
( Labia Majora You keep on talking but it makes no sense at all, Tue 11 May 2010, 11:50, Reply)

Spoken like a true woman.

( Noeli overtheshoulderboulderholderthingstraplatchboobs, Tue 11 May 2010, 12:01, Reply)

You didn't say it isn't you said it can't.
Which is stupid.
(PsychoChomp, Tue 11 May 2010, 11:50, Reply)