**Core Concept**
The commonest reason for adherent labia minora in a newborn is due to the presence of a physiological condition that causes the labia minora to stick together. This condition is often related to the hormonal changes that occur during fetal development and early infancy.

**Why the Correct Answer is Right**
Adherent labia minora in newborns is commonly caused by the presence of maternal estrogen, which is transferred to the fetus during pregnancy. This estrogen causes the labia minora to grow and become more prominent, leading to their adherence. The correct answer is related to this physiological condition, which is a result of the transfer of maternal hormones to the fetus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the physiological condition that causes adherent labia minora in newborns. The condition is not caused by an infection or inflammation.
**Option B:** This option is incorrect because it is not a recognized cause of adherent labia minora in newborns. The condition is not caused by a congenital anomaly or genetic mutation.
**Option C:** This option is incorrect because it does not accurately describe the cause of adherent labia minora in newborns. The condition is not caused by an injury or trauma.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize that adherent labia minora in newborns is a normal physiological condition that resolves on its own within the first few months of life. It is not a cause for concern and does not require any treatment.

**Correct Answer:**
Estrogen from maternal transfer