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Birthweight is below the tenth percentile of average for the gestational age.

Comparison of Symmetric and Asymmetric IUGR Fetuses


Symmetric (20%)

Asymmetric (80%)

Symmetrically small

Normal ponderal index

Head / abdomen and femur / abdomen ratios = normal

a/w genetic disease infection

Total number of cells = less

Cell size = normal

Complicated neonatal course; poor prognosis

Head larger than abdomen

Low ponderal index

Elevated head / abdomen and femur / abdomen ratios

Placental vascular insufficiency



Usually uncomplicated neonatal course and good prognosis

Causes of IUGR



Fetal factors

• Infections (TORCH)

• Malformations

• Chromosomal abnormalities (trisomies 18/13/21)

• Multiple pregnancy










Maternal factors

• Cardiorespiratory disease

• Renal disease, acidosis

• Preeclampsia / hypertension

• Diabetes mellitus

• Anemia, fever

• Drugs

• Smoking, alcohol



Placental factors

• Abruptio placentae

• Thrombosis, infarction (fibrin deposition, APLA syndrome)

• Placentitis, vasculitis, edema

• Chorioamnionitis

• Placental cysts, chorioangioma

• Circumvallate placenta





Fetal growth deficiency









Uterine factors

• Decreased uteroplacental blood flow

• Arteriosclerosis of decidual spiral arteries

• Connective tissue disorders

• Fibroids

• Morphologic abnormalities
























USG Markers for Asymmetric IUGR

  1. Abdominal circumference (on USG) is the best marker for IUGR followed by ponderal index.
  2. Ponderal index (PI) = fetal weight divided by third power of femur length. Normal = 8.3
  3. PI <7 indicates IUGR.
  4. FLI AC = 22% is normal, >23.5% suggests IUGR.
  5. Normally after 34 weeks, HC/AC is less than 1. If it is more than 1 it suggests IUGR.
  1. Fetal glycogen stores from liver are depleted and there is redistribution of blood flow; therefore, AC is smaller than other parameters (BPD and femur length) on USG. FL is not affected by nutrition status.
  2. Color Doppler is the best investigation for the management of asymmetrical IUGR.
  3. Umbilical artery Doppler is considered abnormal if the SID ratio is above the 95th percentile for gestational age (rising S/D ratio is the earliest change in IUGR).
  4. Absent diastolic flow in umbilical artery is an ominous sign, and IUFD can be expected within 7 days.
  5. In extreme cases of growth restriction, end diastolic flow may become reversed and IUFD will occur within 48h.
  6. As the SID ratio begins to rise in fetus with asymmetric IUGR, the blood flow in MCA increases. There is redistribution of blood flow, and vital organs like brain continue to receive adequate blood at the expense of liver and kidney. This is called as BRAIN-SPARING EFFECT.
  7. Absent and reversed diastolic flow in umbilical artery on color Doppler is an indication of immediate LSCS.
  8. Low-dose aspirin is thought to improve the uteroplacental circulation and can be given to patients of IUGR and is also given in subsequent pregnancy to prevent IUGR.
  9. Asymmetric IUGR has better prognosis compared to symmetric IUGR.
  10. Nitroglycerin (NTG) patches can be applied to maternal abdomen to increase the uterine blood flow. This is currently under research/ trials.

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