I recently adopted a female cat who had been a stray. After a few weeks, I noticed signs of pregnancy and have confirmed that the cat is pregnant with 6 kittens. ~2 weeks into gestation before the pregnancy was known, she received the FVRCP vaccine, which is not recommended during pregnancy due to the possibility of cerebellar hypoplasia occurring in kittens. The vet has looked at an ultrasound as well as X-rays and believes the kittens are healthy, but hasn't given any sort of likelihood that the vaccine will cause problems in the kittens.
What is the likelihood that a cat vaccinated early in pregnancy for Panleukopenia will have kittens affected by cerebellar hypoplasia? Is there any research published about probability of birth defects, or is it assumed that any kitten born from a vaccinated mother will almost certainly have abnormalities?