If I can put in my two cents,
I was a TA for Human Sexuality classes before I graduated and this comes up every semester, like slvWriting said, the possibility is so unlikely, besides the fact that the human mouth is a very hazardous place for sperm the 1st 4 inches of the vaginal cavity are almost as hazardous, there are enzymes in the vagina that keep toxins out and sperm would be considered toxic (soory guys) to the vagina
for the most part an excited vagina that has been well lubed is lest hazardous but not to the point where sperm could survive oral and vaginal trips.