Amniotic fluid index

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

Technique

  • the uterus is divided into four imaginary quadrants with the linea nigra and a mediolateral line running through the umbilicus acting as the vertical and the horizontal axes respectively
  • the deepest pocket devoid of an umbilical cord and fetal parts is measured in the vertical dimension
  • measurement of the four pockets is in centimetres
  • the sum of all the four quadrant measurements is the 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 5-25 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 to be oligohydramnios
    • value changes with age: the 5th percentile for gestational ages is most often taken as the cut-off value, and this is around an AFI of 7 cm for second and third-trimester pregnancies; an AFI of 5 cm is two standard deviations from the mean
  • AFI >25 cm is considered to be polyhydramnios
Ultrasound - obstetric
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Article information

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