**Core Concept**
Growth restriction during the intrauterine period is a condition where the fetus does not grow at a normal rate inside the womb. This can be due to various factors such as maternal health issues, placental insufficiency, or genetic conditions. Estimating fetal growth restriction is crucial for timely intervention and management.

**Why the Correct Answer is Right**
The sonographic parameter used to estimate fetal growth restriction is the **Aberdeen Biometry Chart**, also known as the **Customized Growth Assessment**. This method involves plotting the fetal biometric parameters (such as head circumference, abdominal circumference, and femur length) on a chart to determine if the fetus is growing at a normal rate. The customized growth assessment takes into account the gestational age and the mother's medical history to provide a more accurate estimate of fetal growth.

**Why Each Wrong Option is Incorrect**
**Option A:** **Fetal weight estimation** is not a reliable method for estimating growth restriction, as it can be affected by various factors such as maternal obesity and fetal position.

**Option B:** **Crown-rump length** is a parameter used to estimate gestational age, but it is not a reliable indicator of fetal growth restriction.

**Option C:** **Placental thickness** can be a useful parameter in assessing placental function, but it is not a direct indicator of fetal growth restriction.

**Clinical Pearl / High-Yield Fact**
When assessing fetal growth restriction, it is essential to consider the customized growth assessment and not rely solely on a single parameter, as this can provide a more accurate estimate of fetal growth and reduce the risk of false positives or false negatives.

**Correct Answer: C. Placental thickness.**