Obstetric Ultrasound Normal Vs Intrauterine Growth Restriction (IUGR) | Placental Insufficiency USG
IUGR: Intrauterine growth restriction (IUGR) is a condition where a fetus is smaller than expected for the number of weeks of pregnancy.
- Gestational age used to assess fetal growth in cases of intrauterine growth restriction (IUGR) is typically determined based on the last menstrual period (LMP), early first trimester ultrasound (CRL), or a combination of both.
- Biometric Parameters: From 12 week onwards, fetal growth can be assessed by measuring Femur Length (FL), Humeral Length (HL), Biparietal Diameter (BPD), Head Circumference (HC), and Abdominal Circumference (AC). Values of these measurements will correspond to gestational age calculated automatically by the machine. Normal measurements will match the gestational age by LMP. A difference of 1 week can be normal.
- Fetal parameters, such as Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), and Femur Length (FL), are used by the ultrasound machine to calculate Estimated Fetal Weight (EFW).
IUGR Features:
- AC below 3rd percentile
- Estimated Fetal Weight (EFW) below 10th Percentile for gestational age with abnormal doppler findings.
- Oligohydramnios
- HC/AC Ratio is normal in Symmetrical IUGR
- Elevated HC/AC Ratio in Asymmetric IUGR: Greater than 1.3 approx.
- Early maturation of the placenta: A grade 3 placenta seen much earlier in pregnancy
- Umbilical Artery Absent End Diastolic Flow: No waveform produced during end diastole.
- End diastolic Flow Reversal
- Pulsatility Index Greater than 95th Percentile
- Resistive Index: Greater than 0.75
- Low resistance flow in MCA: Significant diastolic flow. Indicates Brain sparing effect
- Middle Cerebral Artery RI of 0.4-0.64 is considered abnormal
- Brain Sparing Effect: The fetus’s body reacts by redirecting more blood to the brain to ensure it gets enough oxygen and nutrients. This is because the brain is the most vital organ for survival and development.
- Abnormal MCA Doppler findings do not directly indicated IUGR. These findings must be used in conjunction with umbilical artery doppler findings.
MCA Pulsatility Index/Umbilical Artery PI
- Abnormal CP Ratio: Less than 1
- Pulsatility in umbilical vein: Waveform shows crests and troughs
- Uterine Artery: Persistence of a Diastolic Notch into 2nd trimester.
- UA PI: Greater than 95th percentile