What does an Amniotic Fluid Index (AFI) of 20.89 indicate?

Amniotic Fluid Index of 20.89 cm: Clinical Significance

An Amniotic Fluid Index (AFI) of 20.89 cm indicates increased amniotic fluid volume but falls within the normal range (5-24 cm) as defined by the American College of Radiology, though it is approaching the upper threshold for polyhydramnios. 1

Understanding AFI Measurement and Normal Ranges

• AFI is measured by summing the deepest vertical pocket of amniotic fluid in each of the four quadrants of the uterus, providing a quasi-quantitative assessment of amniotic fluid volume 1
• The normal range for AFI is 5-24 cm, with values below 5 cm indicating oligohydramnios and values above 24 cm indicating polyhydramnios 1
• AFI values vary throughout pregnancy, with a progressive rise until 26 weeks, followed by relative stability until 38 weeks, after which there is a gradual decline 2, 3

Clinical Interpretation of AFI 20.89

• At 20.89 cm, this AFI value is elevated but still within normal limits, approaching the upper threshold of 24 cm 1
• This value represents approximately:
  • 524 mL of amniotic fluid at 20 weeks
  • 848 mL of amniotic fluid at 30 weeks
  • 723 mL of amniotic fluid at 34 weeks 4
• While not meeting the strict definition of polyhydramnios (>24 cm), this elevated value warrants clinical attention as it approaches the 95th percentile for most gestational ages 5

Clinical Implications and Monitoring

• Although within normal range, an AFI of 20.89 cm may indicate a trend toward excess amniotic fluid that should be monitored 1
• If the current AFI is >8 cm (as in this case), the risk of developing oligohydramnios within 7 days is only 2.2%, suggesting weekly assessments would be adequate for follow-up 6
• AFI is an essential component of the modified Biophysical Profile (mBPP) for ongoing fetal surveillance 1
• The clinical context should be considered, as AFI values vary slightly by maternal race/ethnicity, though these differences may not be clinically significant 5

Considerations for Fetal Assessment

• An elevated but normal AFI should be interpreted alongside other fetal assessment parameters, including estimated fetal weight and Doppler studies 7
• If other parameters are normal, this AFI alone would not typically trigger delivery or intervention before 37 weeks 7
• Continued surveillance with weekly AFI measurements is appropriate given the value is elevated but not meeting polyhydramnios criteria 6

Alternative Measurement Considerations

• Some evidence suggests that the Maximum Vertical Pocket (MVP) may perform better than AFI for clinical decision making 1
• Normal MVP is defined as ≥ 2 cm throughout gestation 1
• Consider incorporating MVP measurement in future assessments as it may result in fewer unnecessary interventions 1