Tetras don't become pregnant, but they can get egg bound. However, the fish in the photo doesn't look egg bound to me, I think there's something else going on. As CaptainBarnicles said, a clearer photo would help.
That is a very sick Pristella, I'm sorry to say. It's a man made colour variety, but is also quite deformed. For comparison, here is how a healthy naturally coloured one looks.