Amniotic Fluid Index (AFI)
An ultrasound procedure used to asses the amount
of amniotic fluid. The amniotic fluid index is measured by dividing the uterus into four
imaginary quadrants (Figure 1). The linea nigra is used to divide the uterus
into right and left halves.The umbilicus serves as the dividing point for the
upper and lower halves.
The transducer is kept parallel to the patient’s longitudinal axis and perpendicular
to the floor. The deepest, unobstructed, vertical pocket of fluid is measured in
each quadrant in centimeters. (Figure 2). The four pocket measurements are then added to
calculate the AFI. Normal AFI values range from 5 to 25 cm [1, 4]. Based
on available data from randomized control trials (RCTs) the American College of
Obstetricians and Gynecologists (ACOG) supports the use of the deepest vertical pocket
of amniotic fluid volume of 2 cm or less to diagnose oligohydramnios rather than
an amniotic fluid index of 5 cm or less .
1. Rutherford SE, Phelan JP, Smith CV, Jacobs N.The four-quadrant
assessment of amniotic fluid volume: an adjunct to antepartum fetal heart rate
testing. Obstet Gynecol. 1987 Sep;70(3 Pt 1):353-6. PMID: 3306497
2. Phelan JP, Smith CV, Broussard P, Small M. Amniotic fluid volume assessment
with the four-quadrant technique at 36-42 weeks' gestation. J Reprod Med. 1987
3.Magann EF, et al Ultrasound estimation of amniotic fluid volume using the largest vertical pocket
containing umbilical cord: measure to or through the cord?
Ultrasound Obstet Gynecol. 2002 Nov;20(5):464-7.PMID: 12423483
4. Phelan JP, et al.Polyhydramnios and perinatal outcome. J Perinatol. 1990 Dec;10(4):347-50.
5. Antepartum fetal surveillance. Practice Bulletin
No. 145. American College of Obstetricians and Gynecologists. Obstet Gynecol