If this was an umbilical hernia - they are quite common in puppies and kittens, and it was probably repaired when the vet did the spay or neuter. I would just ask where the hernia was and see if you can see any evidence of it still existing. (If it's still there, you will see a lump on the tummy or in the area where it was.) Unless it's still there or is huge, your kitten should have no after effects from it. They are usually caused from mom biting the cord too close or pulling too hard when the kitten is born.
Please let me know if I can help further, and congratulations on your new addition!
Feline Healthcare
16 yrs health care mgmt & issues relating to cats, reproductive issues and multicat environments