Seeking info - Black Lab

Question
This past weekend I acquired a dog from an acquaintance that found her as a stray. They had searched for possible owners, but came up empty.  They had planned to put her in a shelter if they could not find a home by the end of this weekend. In any case, after meeting the dog she has a wonderful disposition and we ended up taking her home. The people that found her estimated her to be about 4 months, but my un-educated (but very dog experienced) instinct tells me she's probably closer to 8 months. She has typical teenage dog behavior but not overly exaggerated. She has no scar, so it's apparent that she is not spayed. She has a voracious appetite and is very loving. She seems to have some training (refuses to cross thresholds of doors without being carried for example and she works very good on a leash), so I am inclined to think she had human owners before being let go. After spending 2 days with her, I'm highly suspicious that she's pregnant. She has a voracious appetite and her belly is a little big. She has no difficulties with her digestive tract based upon size and quantity of droppings in the backyard, so I'm not suspecting other ailments (worms) that can explain these symptoms. In any case, long story short, I won't be able to take her for her initial check up (scan for microchip and basic starter exam and to determine if she really is pregnant) until Friday. In the meantime, I am putting some feelers out to get an idea of who might be interested in a puppy. If she is pregnant, I think she's probably at the 4-6 weeks stage so I don't have a lot of time to plan. Given the fact she's really to young to have been pregnant with a litter, can you give me an idea of how many pups to plan for? I'm expecting 3-4 since Labs seem to tend to have litters in the 5-10 size when they are fully mature. I anticipate my vet will answer this for me, but how long after her delivery do I wait before getting her spayed?

Answer
Good luck with your new dog, that's great that you took her in.

Unfortunately, there is NO standard as far as how many pups she'll have...how many has nothing to do with age.  Breed-wise, larger dogs like labs, can have typically 6-12 pups.  And singleton pups are common too.  

Your vet can do a couple of things...there is something called a relaxin test which is a blood test to see if the dog is pregnant.  If she is as far along as you think, they can also do a sonogram to see if there are live pups in there.  

When we bred out last girl for her first time, after her heat (after she was bred), her vulva did not reduce in size like when they are not in heat.  Basically a swollen vulva, but no bleeding.  You can also guess if she is pregnant by her nipples...they tend to get a bit bigger/pinker, and they'll be a gradual loss of hair under the belly.  

This website has some good basic info about pups and whelping:  http://www.debbiejensen.com/