**Question:** IUGR cannot be detected by USG using:

A. Increased amniotic fluid index (AFI)
B. Color Doppler ultrasound
C. Fetal biometry (biparietal diameter, femur length, and abdominal circumference)
D. Transverse diameter of the fetal skull

**Core Concept:**
IUGR, or Intrauterine Growth Restriction, is a condition where a fetus fails to achieve its potential growth due to various causes. Ultrasonography (USG) or ultrasound is a non-invasive diagnostic tool used for fetal growth assessment. In this context, we need to understand the key aspects of USG that can help or hinder the detection of IUGR.

**Why the Correct Answer is Right:**
USG can detect the presence of IUGR by evaluating fetal biometry (biparietal diameter, femur length, and abdominal circumference). These measurements help in assessing fetal growth and comparing it with the expected values based on gestational age. However, increased AFI (amniotic fluid index) is not specific to IUGR and can be influenced by other factors like polyhydramnios, maternal obesity, or placental dysfunction. Using color Doppler ultrasound may provide additional information on placental perfusion, but it is not a definitive method for detecting IUGR. Transverse diameter of the fetal skull is not a standard parameter for assessing fetal growth.

**Why Each Wrong Option is Incorrect:**
Option A (increased AFI) is incorrect because increased AFI can be influenced by various factors that are not specific to IUGR, making it unreliable for detection.

Option B (Color Doppler) is incorrect because while color Doppler ultrasound offers additional information about placental perfusion, it is not a standalone method for detecting IUGR.

Option D (transverse diameter of the fetal skull) is irrelevant to fetal growth assessment as it is not one of the standard parameters used in USG for fetal biometry.

**Clinical Pearl:**
A comprehensive fetal biometry assessment using biparietal diameter, femur length, and abdominal circumference is crucial for detecting IUGR. Assessing AFI and using color Doppler ultrasound can provide additional information, but they are not definitive methods for IUGR diagnosis. It is essential to correlate these findings with clinical and maternal risk factors to make an accurate diagnosis.