Amniotic fluid index

The amniotic fluid index (AFI) is an estimate of the amniotic fluid volume in a fetus. It is part of the fetal biophysical profile

Technique

  • uterus is divided into four imaginary quadrants with linea nigra and umbilicus acting as the vertical and the horizontal axis respectively
  • the deepest pocket devoid of umbilical cord and fetal parts is measured in the vertical dimension
  • measurment of the four pockets is in centimeters
  • sum of all the four quadrant measurements is AFI
  • normal AFI values range from 5 to 25 cm 

Values

The normal range for amniotic fluid volumes varies with gestational age. Typical values include:

  • AFI between 8-18 cm is considered normal; median AFI level is ~14 cm from week 20 to week 35, after which the amniotic fluid volume begins to reduce
  • AFI <5 cm is considered as oligohydramnios
    • value changes with age: the 5th percentile for gestational ages is most often taken as the cutoff value, and this around an AFI of 7 cm for second and third trimester pregnancies; and AFI of 5 cm is two standard deviations from the mean
  • AFI >20-24 cm is considered as polyhydramnios
Ultrasound - obstetric
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Article information

rID: 13597
System: Obstetrics
Section: Approach
Synonyms or Alternate Spellings:
  • Amniotic fluid index (AFI)
  • AFI

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Cases and figures

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    Case 1: AFI measurements
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    Case 2: normal AFI
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    Case 3: polyhydramnios
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