**Core Concept**
Congenital toxoplasmosis is caused by *Toxoplasma gondii* and results from maternal infection during pregnancy. Diagnosis in newborns relies on detecting specific immunoglobulins in cord blood or amniotic fluid, with IgM being key for active infection, while IgG indicates prior exposure and immunity.

**Why the Correct Answer is Right**
IgG antibodies are not diagnostic of congenital toxoplasmosis because they reflect maternal immunity and do not indicate active infection in the fetus. IgM in cord blood is the primary marker for active congenital infection. IgA, though less commonly used, can be more sensitive than IgM in some cases, and "not recalled" refers to the absence of recall of prior infection. Thus, stating IgG is diagnostic is false.

**Why Each Wrong Option is Incorrect**
Option A: IgA is better than IgM in detection — This is incorrect because IgM is the gold standard; IgA is not routinely preferred or more sensitive.
Option B: Diagnosed by detection of IgM in cord blood — This is correct; IgM in cord blood is a hallmark of congenital toxoplasmosis.
Option D: Not recalled — This is correct; the term "not recalled" refers to the absence of a prior maternal infection, which is clinically relevant.

**Clinical Pearl / High-Yield Fact**
In congenital toxoplasmosis, IgM in cord blood is the key diagnostic marker; IgG only indicates maternal immunity and is not diagnostic of fetal infection. Always check for IgM in cord blood, not IgG.

✓ Correct Answer: C. IgG is diagnostic