**Question:** Increased nuchal fold thickness is a feature of –

A. Down syndrome
B. Turner syndrome
C. Edwards syndrome
D. Patau syndrome

**Core Concept:**
Nuchal fold thickness refers to the thickness of the skin fold that lies between the back of the neck and the first pair of cervical vertebrae, measuring the thickness of the subcutaneous tissue. In the context of prenatal ultrasound, measuring nuchal fold thickness is a routine part of the first trimester screening for chromosomal abnormalities.

**Why the Correct Answer is Right:**
Increased nuchal fold thickness is a feature of trisomy 21, which refers to the presence of an additional copy of chromosome 21, leading to Down syndrome (DS). Down syndrome is caused by the presence of an additional chromosome 21, resulting in the clinical manifestations observed.

**Why Each Wrong Option is Incorrect:**
A. Down syndrome is not associated with Turner syndrome, which results from the partial or complete absence of one X chromosome. Turner syndrome is characterized by short stature, gonadal dysgenesis, and distinct clinical features.
B. Down syndrome is not associated with Edwards syndrome, which is caused by a translocation of chromosome 18 to another chromosome. Edwards syndrome results in severe growth retardation, microcephaly, and multiple congenital anomalies.
C. Down syndrome is not associated with Patau syndrome, which is caused by a translocation of chromosome 13 to another chromosome. Patau syndrome leads to characteristic features and severe growth retardation.

**Clinical Pearl:**
Measurement of nuchal fold thickness is a non-invasive method for the early detection of chromosomal abnormalities, particularly Down syndrome. It is part of a comprehensive prenatal screening panel that includes other markers such as maternal age, first-trimester serum markers, and ultrasound findings. Early detection allows for appropriate counseling and management of the fetus and the family involved, leading to better outcomes and support.