Risk of congenital toxoplasmosis in women with low or indeterminate anti-Toxoplasma IgG avidity index in the first trimester of pregnancy: an observational retrospective study

Congenital toxoplasmosis (CT) affects 1-10 fetuses/10,000 live newborns in western countries. Without knowing pre-conception serostatus, it is hard to date the infection when anti-Toxoplasma IgG and IgM antibodies are positive at first screening. While a high IgG avidity index (AI) in the first trimester excludes CT, the same cannot be said of intermediate and low AI. The aim of this study was to estimate the risk of CT when intermediate or low AI is detected in the first trimester of pregnancy.