My 10 mo. chihuahua just finished her first heat cycle.  My male was nuetuered in April.  On several occasions I have seen them mating. Now she is displaying signs of pregancy.  I don't know how that could be, but i have noticed my male still ejaculates. Is it possible the didnt nueter him correctly and now shes pregnant?

i had a friend that had that hapen to her. they dident nuter her male correcly and her female had a litter of pups with him.

what did the vet say???

I havent taken her the vet yet my aunt is a vet and i want her to check her out in about a week   plus my story has a jerry springer twist they are brother and sister but not from the same liter

Far more likely that she is having a phantom, but because of his activities it is possible thet she has an infection so I would take her to the vet for a check up anyway.

Are male dogs the same as men, in that they can still be fertile for a short while after neutering, after all April isn't that long ago....

That is possible, the thing that would concern me is that some castrated males can still perform the mating act but are not fertile, but the very act of mating can introduce infection into the female and think that what ever the bitch has wrong, be it pregnant, phantom or Pryo she needs to see a vet, and sooner rather than latter.