I definitely understand the questions you are asking. They are hard, indeed.
In my thinking, aborting a confirmed psychopathic-brained-fetus would be hard to justify if one is at all pro-life. Aborting the pregnancy on the grounds that the baby could grow up to be a serial killer and bring grief to the parents and society sounds frighteningly close to the arguments about unborn Down’s babies (minus the whole serial killer thing).
Either we all have a right to life, or we don’t.
Furthermore, can you punish someone for a crime which they have not yet committed? I highly recommend watching the movie Minority Report, it is very thought provoking.
If our legal system says innocent until proven guilty, that applies to psychopaths too, and if it is that way in the courts then it should be in the womb, too.
The question you ask is valid, but the pain/suffering of the parents and the potential burden on society arguments are tenuous, especially if you are pro-life.
In my opinion, it is wrong to kill a baby based on the fact that their brain structure suggests that they will probably be serial killers. The death penalty is reserved for offenders, not potential offenders.
I watched a Youtube video of a brain researcher explaining that he had found markers in the brains of psychopaths which could be measured. His mother took him aside and told him he was in no position to talk about such things since their own family tree contained a psychopath or two. He researched and found he was indeed related to one more two psychopaths. So he had his own brain imaged and found some markers associated with psychopathy. So the question moved to what environmental element made the difference in his life that he had not become a psychopath.