I have a bitch on day 59 from first mating -vet who scanned thought she had taken from the second mating 4 days later so more likely 55 days. (Dog was not interested the following 3 days hence second mating so much later.) She is getting huge, bigger than I had expected (first litter). This afternoon she has suddenly become incontinent. It has happened twice now. She sleeps, gets up and where she has been there is a puddle and she drips as she walks along. (Definitely urine.) I have never had this happen before. She's been out for a wee more or less every hour and a half. Could this be just because she is carrying a big heavy load, or should we go straight to the vet in case she has a urinary tract infection?

Maybe take sample to vet rather than take her?

I had this with my bitch while pregnant she was not particularly big, but towards the end I was literally following her round with a mop. I took a urine sample in to the vet and they did tests and also sent a sample to the laboratory for testing and to grow a culture. All came back normal.
She whelped 9 large puppies, and was still not able to hold on for long, sometimes had wet before I could unlock the door, but a couple of weeks after whelping she went back to her pre-pregnancy routine.
Now 9 weeks after her puppies were born, everything is fine, but I think I need to invest in some new carpet !! Good job I had vinyl laid in most areas.
Would definitely take a urine sample in to the vets just for peace of mind. When I had my bitch scanned the vet said it looked like the pups were pressing around the bladder.

The first thing that comes to mind is pressure on the bladder.  Then I read dorcas' post!  I would prefer to take a sample of wee in rather than take your bitch. 

Then you can bet that she'll whelp before the results are back!  :-)

We phoned the vet yesterday and they said it could be the pressure of the pups or it could be a number of other reasons, so either wait and see or bring her in. As she wasn't acting like she had a UTI (i.e. did not keep going on purpose) I decided to wait, because the problem was, we'd not be able to get a urine sample as her bladder kept emptying all the time so by then was empty! Later yesterday evening it seemed to stop all of a sudden, so maybe pups had moved about? She was asleep on the floor right now and I just called her to me and the floor beneath her was dry!

Hope that's her sorted :-)