**Core Concept**
Increased nuchal translucency (NT) at 14 weeks of gestation is an ultrasound marker that indicates an increased risk of aneuploidy, particularly Down syndrome (Trisomy 21), Turner syndrome, and other chromosomal abnormalities. The NT thickness is measured between the skin and the soft tissue of the back of the fetal neck.

**Why the Correct Answer is Right**
The increased NT thickness is associated with an increased risk of aneuploidy due to the impaired fetal development and the resulting accumulation of fluid in the subcutaneous tissue of the neck. This condition is thought to be related to the altered expression of genes involved in the development of the neural crest and the resulting abnormalities in the formation of the lymphatic and venous systems. The increased NT is also associated with an increased risk of fetal cardiac abnormalities and other congenital anomalies.

**Why Each Wrong Option is Incorrect**
* **Option A:** Increased NT at 14 weeks of gestation is not typically associated with gestational diabetes mellitus.
* **Option B:** While increased NT can be associated with an increased risk of aneuploidy, it is not a direct indicator of fetal cardiac abnormalities.
* **Option C:** Increased NT at 14 weeks of gestation is not typically associated with placental insufficiency.

**Clinical Pearl / High-Yield Fact**
In the first trimester, increased nuchal translucency is a significant marker for aneuploidy and other congenital anomalies, and it should prompt further evaluation with non-invasive prenatal testing (NIPT) and detailed fetal anatomy ultrasound.

**Correct Answer:** D.