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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 .


Figure 1. Figure 2.


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 Jul;32(7):540-2.PMID: 3305930
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.
PMID: 2277279

5. Antepartum fetal surveillance. Practice Bulletin No. 145. American College of Obstetricians and Gynecologists. Obstet Gynecol 2014;124:182–92.PMID: 24945455

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