[Dating anti-Toxoplasma IgM in pregnancy using VIDAS-ELFA methods].

Background: To study the usefulness of IgG and IgM titration, and avidity of IgG to date IgM anti-Toxoplasma gondii.
Methods: VIDAS Toxo IgG, VIDAS Toxo IgM and VIDAS Toxo IgG Avidity tests were used. 64 sera containing both IgM and IgG T. gondii antibodies were analyzed, 32 from 12 individuals infected 40 weeks previously (group I), and the remainder from 17 individuals with an infection of more than 40 weeks (group II).
Results: An IgM index < 1.05 was associated with an infection > 12 weeks. An avidity index > 0.164 excluded 100% infections of < or = 12 weeks. Avidity indexes > 0.26 and 0.45 excluded infections of < or = 20 and < or = 40 weeks, respectively.
Conclusions: The serology methods used in this study can adequately identify residual IgM anti-T. gondii, often avoiding the need of a new blood extraction to analyze IgG kinetics in pregnant women.