**Core Concept**
The diagnosis of chlamydial infection in newborns involves identifying the infection in the baby, which can be caused by the mother's transmission during delivery. Chlamydia trachomatis is a sexually transmitted bacterium that can be vertically transmitted to the fetus during pregnancy, leading to neonatal chlamydial infection.

**Why the Correct Answer is Right**
The correct sample to be taken for diagnosis in a baby born to a patient suspected of chlamydial infection is the conjunctival swab. This is because Chlamydia trachomatis can cause conjunctivitis in newborns, which is a common presentation of neonatal chlamydial infection. The conjunctival swab is a non-invasive sample that can be easily obtained and is highly sensitive for detecting the presence of Chlamydia trachomatis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Blood sample - While a blood sample can be used for some infections, it is not the preferred sample for diagnosing chlamydial infection in newborns.
* **Option B:** Urine sample - Urine samples are used to diagnose chlamydial infection in adults, but are not the preferred sample for newborns.
* **Option C:** Nasopharyngeal swab - Nasopharyngeal swabs are used to diagnose respiratory infections, not chlamydial infection.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that neonatal chlamydial infection can cause conjunctivitis and pneumonia, and prompt diagnosis and treatment are crucial to prevent long-term complications.

**Correct Answer:** C. Nasopharyngeal swab