The commonest route of transmission of HIV from the mother to the baby is –
**Core Concept**
During pregnancy, lactation, or postpartum, HIV can be transmitted from mother to child through various routes. The most common route of transmission is a critical concept in preventing mother-to-child transmission (PMTCT) of HIV.
**Why the Correct Answer is Right**
The correct answer is vertical transmission, specifically through the placenta during pregnancy. This occurs when the virus is present in the maternal blood and crosses the placental barrier, infecting the fetus. The risk of transmission is highest during the third trimester and during labor, especially if the mother is not on antiretroviral therapy (ART). The use of ART and elective cesarean section can significantly reduce the risk of vertical transmission.
**Why Each Wrong Option is Incorrect**
* **Option A:** Intrapartum transmission refers to the transmission of HIV from mother to child during labor or delivery. While it is a significant risk factor, it is not the most common route of transmission.
* **Option B:** Breast milk transmission, also known as postnatal transmission, occurs when the baby is infected through breast milk. This is a significant route of transmission, especially in settings where safe alternatives to breastfeeding are not available. However, it is not the most common route of transmission.
* **Option C:** This option is not a valid route of transmission.
**Clinical Pearl / High-Yield Fact**
To reduce the risk of mother-to-child transmission, all pregnant women with HIV should be started on ART as soon as possible. This can significantly reduce the viral load in the mother's blood, thereby reducing the risk of transmission.
**Correct Answer: C. Vertical transmission, specifically through the placenta during pregnancy.**