I know a vet who told me she helped a momma cat in litter birth. She was having a real hard time delivering. She gave birth to a "two headed" kitten that wassill born and the mamma couldn't pass the kitten because of the large size of the head. According to this vet this happens more than we know. The rest of the litter was delivered just fine. She chose not to tell the family about the malformed kitten.