Toxoplasmosis in pregnancy — DTM&H MCQ

Correct answer: D — Infection acquired before pregnancy with no risk to the fetus

The correct answer is D, infection acquired before pregnancy with no risk to the fetus. High IgG avidity confirms a mature antibody response, which develops from about 12 to 16 weeks after primary infection; this excludes infection within the preceding three to four months and, at 32 weeks, places acquisition before conception. Toxoplasma IgM can persist for many months to over a year after primary infection, so isolated IgM positivity is not diagnostic of recent infection and must be interpreted alongside avidity. Because infection predates pregnancy and she is immunocompetent, there is no ongoing parasitaemia and thus no transplacental transmission risk. This IgM/IgG-positive, high-avidity pattern is the classic reassurance result in antenatal toxoplasma serology, requiring no further intervention. Why the other options are wrong: A, Acute primary toxoplasmosis acquired during pregnancy: excluded by high avidity, which rules out infection within the last three to four months; acute infection shows low or equivocal avidity. B, Acute infection requiring immediate termination: there is no acute infection, and even confirmed acute toxoplasmosis in pregnancy is managed with spiramycin or pyrimethamine-sulfadiazine plus fetal monitoring, never automatic termination. C, Reactivation of latent toxoplasmosis posing high fetal risk: clinically significant reactivation with fetal transmission occurs almost exclusively in immunocompromised women (e.g. advanced HIV), not immunocompetent hosts, and is not reflected by this serology pattern. D, False positive serology requiring repeat testing: the results are internally consistent (IgM, IgG and high avidity all concordant with past infection), giving no reason to suspect assay error. Key point: High IgG avidity with positive IgM and IgG confirms infection over three to four months old, placing it before conception and excluding fetal risk.

Reference: Teimouri A, Mohtasebi S, Kazemirad E, Keshavarz H. Role of Toxoplasma gondii IgG Avidity Testing in Discriminating between Acute and Chronic Toxoplasmosis in Pregnancy. J Clin Microbiol. 2020 (PMC7448626), https://pmc.ncbi.nlm.nih.gov/articles/PMC7448626/