Amniotic fluid index (AFI)
This is used as an estimate of the amniotic fluid volume, to know if there is a normal amount of amniotic fluid or if there is not enough or too much amniotic fluid.
This is measured by ultrasound and basically is the sum of all the four single deepest pockets from each quadrant.
Note: A fluid pocket may contain fetal parts or umbilical cord loops, but these are not included in the measurement.
Color Doppler
– Used to verify that no umbilical cord is included in the measurement
Measured by:
- Dividing the uterus into four imaginary quadrants
– Linea nigra, divide into right and left halves.
– Umbilicus, divide into upper and lower halves.
- The transducer, is kept parallel to the patient’s longitudinal axis and perpendicular to the floor
- The pockets, are the deepest, unobstructed, vertical pocket of fluid which are measured in each quadrant in centimeters
The normal range for amniotic fluid volumes varies with gestational age.
Amniotic fluid index (AFI) Values
Normal: AFI between 5-24 cm
Mean AFI: ~ 12-15 cm from week 16 to 40
Median AFI level is ~14 cm from week 20 to 35, after which the amniotic fluid volume begins to reduce
Oligohydramnios: AFI <5 cm
Polyhydramnios: AFI >24 cm