**Core Concept**
Adipocere formation is a process that occurs in the decomposition of the human body, particularly in the presence of moisture. It involves the hydrolysis of fats into glycerol and fatty acids, which then combine with calcium and magnesium ions to form a soap-like substance.

**Why the Correct Answer is Right**
Adipocere formation is typically seen in bodies that have been submerged in water or have been exposed to high humidity for an extended period. The process is facilitated by the presence of bacteria that break down the fatty tissues. In the case of a dead-born fetus, adipocere formation is less likely to occur due to the dry environment of the uterus and the lack of exposure to moisture. As a result, the fetus may not show signs of adipocere formation.

**Why Each Wrong Option is Incorrect**
**Option A:** Rigor mortis at birth refers to the stiffening of the muscles, which can occur in a dead-born fetus. This is a possible sign of death and is not related to adipocere formation.
**Option C:** Maceration is the softening and disintegration of the skin and tissues, which can occur in a dead-born fetus due to the loss of amniotic fluid. This is a possible sign of fetal death and is not related to adipocere formation.
**Option D:** Mummification is the desiccation of the body, which can occur in a dry environment. While this is a possible outcome in a dead-born fetus, it is not directly related to adipocere formation.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, the presence or absence of adipocere formation can be an important indicator of the circumstances surrounding a body's discovery. For example, the presence of adipocere in a body found in a wooded area may suggest that the body was submerged in a nearby stream.

**✓ Correct Answer: B. Adipocere formation**