In second trimester of pregnancy, the diagnosis of IUGR can be best made by assessing which of the following parameter?

**Core Concept**
The diagnosis of Intrauterine Growth Restriction (IUGR) in the second trimester of pregnancy involves assessing the fetal size and growth parameters to identify potential issues with fetal development. This requires careful evaluation of various fetal and maternal factors.

**Why the Correct Answer is Right**
The correct answer is **C. Abdominal Circumference (AC)**. The abdominal circumference is a critical parameter in assessing fetal growth and development, particularly in the second trimester. It is measured via ultrasound and is used to calculate the fetal weight and estimate the gestational age. Abnormal values may indicate IUGR. The abdominal circumference is a reliable indicator of fetal growth restriction because it is less affected by changes in the amniotic fluid volume compared to other parameters like the biparietal diameter (BPD).

**Why Each Wrong Option is Incorrect**
* **Option A:** The femur length is a parameter used in fetal growth assessment, but it is not the most reliable indicator of IUGR in the second trimester. Femur length can be affected by various factors, including changes in the amniotic fluid volume.
* **Option B:** The head circumference is an important parameter in fetal growth assessment, particularly in the third trimester. However, it is not the best parameter for diagnosing IUGR in the second trimester.
* **Option D:** The maternal weight is not a reliable parameter for diagnosing IUGR. While maternal weight can provide some information about fetal growth, it is not a direct measure of fetal size and growth.

**Clinical Pearl / High-Yield Fact**
Fetal abdominal circumference is a key parameter in diagnosing IUGR, and its measurement should be performed at least once in the second trimester to identify potential growth restriction.

**Correct Answer:** C. Abdominal Circumference (AC)