Momma cat may already be pregnant

The momma cat started hissing and raising hell toward
her four month old kittens, then she went missing for
seven days. Now that she's back she looks like she has a
buldge and she's passing gas like the last time she was
pregnant. I had planned to get her fixed, but expected it
would be at least a few more months before I had to worry
about her going into heat. She cries to go out then stays
gone anywhere from eight to twelve hours each day.

If she is pregnant, and I take her to get fixed, how much of
a problem would it be to abort her pregnancy? It has been
extremely difficult to give away the three kittens, and there
are still three left. Not many people are interested in kittens.