**Core Concept**
The transmission of HIV from mother to child, also known as mother-to-child transmission (MTCT), is a significant concern in obstetrics. The primary route of transmission is through the exchange of bodily fluids, particularly during vaginal delivery.

**Why the Correct Answer is Right**
Vaginal delivery is the most common and effective route of HIV transmission to the newborn. This is because the virus is present in high concentrations in the genital tract and can be transmitted to the baby during passage through the birth canal. The risk of transmission is higher if the mother has an active viral load, is not on antiretroviral therapy, or has a history of sexually transmitted infections.

**Why Each Wrong Option is Incorrect**
**Option A:** Lower Segment Caesarean Section (LSCS) is a surgical delivery method that reduces the risk of HIV transmission by minimizing contact between the baby and the mother's genital tract. However, it does not eliminate the risk entirely if the mother has an active viral load.

**Option C:** Perinatal transmission refers to the period around birth, including delivery and the first few weeks of life. While it is a critical period for potential HIV transmission, it is not a specific route of transmission.

**Option D:** Breastfeeding is another potential route of HIV transmission, particularly if the mother has an active viral load. However, it is not the most common or effective route of transmission.

**Clinical Pearl / High-Yield Fact**
It is essential to note that antiretroviral therapy (ART) can significantly reduce the risk of HIV transmission from mother to child. In fact, studies have shown that ART can reduce the risk of transmission by up to 95%.

**Correct Answer:**
✓ Correct Answer: B. Vaginal delivery