**Core Concept**
Congenital syphilis refers to the transmission of syphilis from a mother to her child during pregnancy or childbirth. It is a significant public health concern due to its potential to cause severe morbidity and mortality in newborns. The diagnosis of congenital syphilis relies on the detection of treponemal antibodies in the infant's blood, which can be challenging due to the presence of passively transferred maternal antibodies.

**Why the Correct Answer is Right**
The correct answer is **A. VDRL (Venereal Disease Research Laboratory) test with a titer that is at least four times the maternal titer**. This is because the VDRL test measures the level of non-treponemal antibodies, which are typically higher in infants with congenital syphilis. However, in the first few months of life, the infant's VDRL titer may still be elevated due to passively transferred maternal antibodies. Therefore, a titer that is at least four times the maternal titer is considered diagnostic of congenital syphilis.

**Why Each Wrong Option is Incorrect**
**Option B:** **Rapid Plasma Reagin (RPR) test is not specific enough for diagnosing congenital syphilis**. While the RPR test is a non-treponemal test similar to the VDRL test, it is less specific and can produce false-positive results.

**Option C:** **Treponema pallidum particle agglutination assay (TP-PA) is not typically used for diagnosing congenital syphilis**. TP-PA is a treponemal test that detects antibodies to Treponema pallidum, but it is not typically used for diagnosing congenital syphilis due to the presence of passively transferred maternal antibodies.

**Option D:** **Fluorescent treponemal antibody absorption (FTA-ABS) test is not used for diagnosing congenital syphilis**. FTA-ABS is a treponemal test that detects antibodies to Treponema pallidum, but it is not typically used for diagnosing congenital syphilis due to the presence of passively transferred maternal antibodies.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the diagnosis of congenital syphilis can be challenging, and a high index of suspicion is necessary. A thorough physical examination, including a careful assessment of the infant's skin, bones, and nervous system, is crucial in making the diagnosis.

**Correct Answer: A. VDRL (Venereal Disease Research Laboratory) test with a titer that is at least four times the maternal titer**