**Core Concept:**

Cephalic index is a measurement used to describe the head shape of an individual, particularly in forensic anthropology and prenatal diagnosis. It is calculated by dividing the length of the head (cephalic length) by the maximum width of the head (cephalic width), and multiplying by 100 to obtain a percentage value. A normal cephalic index falls between 70-80%.

**Why the Correct Answer is Right:**

Cephalic index is used for assessing the cranial vault asymmetry in fetuses, helping to diagnose certain genetic disorders like Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). In these conditions, the head shape is characteristic and can be detected by calculating the cephalic index. This helps in early diagnosis, prenatal counseling, and management planning.

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because cephalic index is not used for assessing fetal growth and development, which is instead monitored by the biparietal diameter and femur length.

B. This option is incorrect as cephalic index is used for identifying genetic disorders, not assessing brain maturity or cognitive development in fetuses.

C. This option is incorrect because cephalic index is used in forensic anthropology for identifying a specific population or ethnic group, not for diagnosing specific genetic disorders.

D. This option is incorrect because cephalic index is used in prenatal diagnosis, not for determining sex or assessing external genitalia.

**Clinical Pearl:**

Understanding cephalic index can be crucial in prenatal diagnosis and identifying certain genetic disorders. Awareness of the normal range and characteristics of cephalic index can lead to early detection of congenital anomalies and facilitate appropriate management planning for both the fetus and family.