Which confirmatory test is most appropriate for determining if a pregnant woman has a recent toxoplasmosis infection?

The most appropriate confirmatory test for determining if a pregnant woman has a recent toxoplasmosis infection is the test that assesses the avidity of IgG antibodies. This is because the avidity test can differentiate between recent and past infections based on the strength of the binding of IgG antibodies to Toxoplasma gondii antigens.

In cases of recent infection, IgG antibodies are typically low in avidity, meaning they do not bind strongly to the antigen. Over time, following a primary infection, the avidity of these antibodies increases as the immune system matures and produces higher affinity antibodies. Therefore, a low avidity IgG indicates that the infection is likely recent, while a high avidity IgG suggests that the infection occurred some time ago.

In contrast, other tests such as PCR on amniotic fluid can detect the presence of the parasite but do not provide information about the timing of the infection. IgM tests, while useful for initial screening, are less reliable due to potential false positives and require confirmation of a recent infection through other means. Culture of amniotic fluid is not commonly used for this purpose as it is time-consuming and may not yield timely or reliable results.

Thus, the use of IgG avidity