Final answer:
The avidity result is determined using both Titers of antibody in preinfection and postinfection specimens and Amniotic fluid versus serum.
Step-by-step explanation:
The avidity result is determined using both B and C. Avidity is the total strength of all interactions in an antibody-antigen complex, and it is influenced by the affinity between the antibody and the antigen as well as the structural arrangements of the epitope and the antibody's variable regions. To determine the avidity, both the titers of antibody in preinfection and postinfection specimens (option B) and the comparison between amniotic fluid and serum (option C) are considered.