Foetal infection of a pregnant woman with syphilis can be diagnosed by:

Correct option is D

Ans. (d) Polymerase Chain Reaction (PCR) test
Solution:
Polymerase Chain Reaction (PCR) is the most sensitive and specific test for diagnosing foetal syphilis infection. It works by detecting the DNA of Treponema pallidum (the bacterium causing syphilis) in amniotic fluid, umbilical cord blood, or fetal tissue.
Explanation of Options:
1. ELISA (Enzyme-Linked Immunosorbent Assay)
· Detects antibodies against Treponema pallidum.
· Useful for maternal screening but not for diagnosing foetal infection, as maternal antibodies can cross the placenta.
2. Western blot
· Identifies specific syphilis antibodies, used as a confirmatory test for syphilis in the mother.
· Cannot detect active foetal infection.
3. Coomb’s test
· Used for haemolytic diseases of the newborn (e.g., Rh incompatibility).
· Not relevant for syphilis detection.
4. PCR (Polymerase Chain Reaction) – Correct Answer
· Directly detects Treponema pallidum DNA, making it highly sensitive and specific.
· Can be performed on amniotic fluid, placental biopsy, or neonatal blood samples to confirm intrauterine transmission.
· Can detect syphilis even before symptoms appear in the newborn.
Thus, PCR is the most reliable diagnostic test for detecting foetal infection with syphilis in pregnant women.