How can you tell when a dog is pregnant?

My friend has two rottweilers who are siblings. Their names are baby and boomer. Well baby just got her first heat, so i told my friend to keep them apart and to get baby spayed. well that was last week, and yesterday my friend told me she thinks baby is pregnant. I really didn't want them to breed, neither did she. I was wondering if there is any signs and what to do if she does have puppies. I know the puppies might have some sort of problems b/c the parents are siblings. I asked my friend if she has noticed anything in baby's appearance. she said that she is gaining weight and that her nipples are getting larger and firmer. I know she has a chance of having a false pregnancy or something. All info will be helpful. Please don't turn this into an arguement thread, I just need help.

Theres a possible chance she still can be spayed if its early enough in the pregnacy. tell her to take the vet as soon as possible to have it checked out.

but there is no way of really knowing if shes preg or not untill she starts to become fat without a vet telling you otherwise. from your description.. sounds like she is though. :(

Its nearly impossible to tell this early, espcially if she is still in heat. Even if she's not pregnant, she can still display signs OF pregnancy, such as lactating nipples, etc. Jamie went through something similar and gave me a scare, but she ended up NOT being pregnant.

If she is still in heat, she CAN NOT be spayed until its over.

The only way to tell for 100% certain, aside from time and waiting it out, is to bring her to the vet!

For reference though when Jamie went through her heat, her nipples got large and hard and gained some weight, too. But its a part of the normal cycle I assume and a week later she went back to normal.

I told her about everything you said and even directed her to this thread. I don't see her till monday so i had to just email the information to her. I'll let you know what she says/does. thanks for the info :)

It's impossible to tell without asking the vet --- The vet knows what to feel for when feeling around the tummy. Visa's breeder had a dog that she had bred that never turned out to be pregnant, even when she was to give birth in two weeks. That's how hard it can be to tell sometimes.