littermates mated!

Question
Hello and thank you for your time and expertise. One year ago I adopted two stray kittens from my local vet.  I have been around cats all my life and I estimate these two little orphans were about 6 weeks old.  They were saved from a trash bin.  It is obvious they are littermates; both are grey tabby male has sleek fur and his sis has the same colors but is more fluffy.  They are healthy, strong, and happy indoor cats. I have had the male neutered, but . .  .with NO WAY this lil girl kitty has had contact with any adult males, we must have waited a bit too long.  So, we are expecting.  And worried.  She has chosen her queening zone, has some milk, and her babies are moving.  I assume it is almost time.  We have been feeding her as much of anything she wants, giving her a choice of dry foods, table scraps, and making certain she always has access to high-quality foods.  She wants to be in her nest and seems to want me nearby at all times.  She is preening and resting quite a lot.  What kinds of problems should I anticipate?  I have acted as midwife for scores of kittens, so I know the basics.  Should her kittens be normal?  Any reason for me to get her to a vet as soon as labor starts?  What are the odds, in general, for survivability of the kittens . . . ?  Please help.  We had the male neutered when she had her first heat, however, somehow he seems to have mated with her in her next cycle . ??  I know he went through the motions . . .Thank you again, Very Worried Mom

Answer
Hi Teresa
The male cat can produce sperm for up to 45 days after the operation. So maybe he mated with her after the operation and was successful. Now count 65 days from then and the litter will be due around that time.
Brother and sister mating is not ideal and may I repeat may cause malformed or dead kittens at the end of the term. However there have been many successes in this close mating particular in breeds that only have small numbers of examples. So watch her carefully. If she goes into distress during labour then you may have to go to the vet and let him try the two options he has. Option one is Oxytocin to induce expelling of the kittens. If that fails he would then consider a caesarian section to deliver the kittens that way
Now the chances are she may lose some or all of the litter , those that survive should be neutered to prevent a re occurrence.
I wish you well and hope the little mother does well
Regards

Ray