**Core Concept**
Intrauterine Growth Restriction (IUGR) refers to the failure of a fetus to achieve its growth potential due to placental insufficiency or maternal factors. This condition is characterized by a decrease in fetal weight and/or abdominal circumference below the 10th percentile for gestational age.

**Why the Correct Answer is Right**
IUGR is primarily caused by placental insufficiency, which results from inadequate maternal-fetal blood flow and oxygen delivery to the placenta. This leads to decreased nutrient and oxygen transfer to the fetus, ultimately causing growth restriction. The placenta's ability to produce growth factors, such as human placental lactogen (hPL), is impaired, further contributing to IUGR.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while maternal hypertension is a risk factor for IUGR, it is not the primary cause. Maternal hypertension can lead to placental insufficiency, but other factors such as maternal malnutrition, smoking, and pre-existing medical conditions also play a role.
**Option B:** This option is incorrect because while fetal anomalies can contribute to IUGR, they are not the primary cause. Fetal anomalies can lead to growth restriction, but the underlying issue is often placental insufficiency.
**Option C:** This option is incorrect because while maternal diabetes is a risk factor for fetal macrosomia, it is not directly related to IUGR. Maternal diabetes can lead to fetal macrosomia due to increased glucose and insulin levels, but it does not cause IUGR.

**Clinical Pearl / High-Yield Fact**
In cases of suspected IUGR, it is essential to assess fetal growth velocity and monitor for signs of placental insufficiency, such as maternal hypertension and proteinuria. Regular ultrasound assessments and Doppler studies can help identify IUGR and guide management.

**Correct Answer:** D