Amniotic Fluid Index (AFI) 

Overview: 

Amniotic fluid index (AFI) is an estimate of the amount of amniotic fluid and is an index for fetal well-being. When the fetus receives inadequate nutrients and oxygen from the placenta, blood is shunted away from the fetal kidney, glomerular filtration rate decreases, and urinary output decreases. Therefore, decreased amniotic fluid volume due to decreased urine production by the fetal kidney is a reflection of chronic hypoperfusion of the fetus. 

1. AFI Score

AFI is the score (expressed in cm) given to the amount of amniotic fluid seen on ultrasonography of a pregnant uterus. To determine the AFI, doctors may use a four-quadrant technique, when the deepest, unobstructed, vertical length of each pocket of fluid is measured in each quadrant and then added up to the others, or so called “Single Deepest Pocket” technique. 

• An AFI between 8-18 is considered normal. Median AFI level is approximately 14 from week 20 to week 35, when the amniotic fluid begins to reduce in preparation for birth. 

• An AFI less than 5 is considered Oligohydramnios. The exact number can vary by gestational age. The fifth percentile for gestational age is sometimes used as a cutoff value. 

• An AFI > 20-24 is considered Polyhydramnios. 

Why is AFI important to the NICU RT? 

• Fetal Lung Development: The AFI is a measure of the amniotic fluid surrounding the fetus. A sufficient amount of amniotic fluid is crucial for fetal lung development. The NICU RT needs to be aware of the AFI to anticipate potential respiratory issues in the neonate. Inadequate amniotic fluid levels may suggest an increased risk of pulmonary hypoplasia, a condition in which the lungs do not develop properly. 

• Risk of Meconium Aspiration: A low AFI may be associated with meconium-stained amniotic fluid, indicating that the fetus has passed stool in utero. Meconium aspiration can lead to respiratory distress in the newborn. RTs in the NICU should be prepared to manage respiratory distress and potential complications associated with meconium aspiration syndrome. 

• Preterm Birth Risk: Abnormal AFI levels, especially if low, may be indicative of conditions such as oligohydramnios, which is associated with an increased risk of preterm birth. Preterm infants often face respiratory challenges, and NICU RTs should be ready to provide respiratory support to these vulnerable newborns. 

• Identification of Fetal Anomalies: An abnormal AFI may be associated with certain fetal anomalies or conditions. Some congenital abnormalities can affect the neonate's respiratory system. Knowledge of the AFI and its correlation with potential anomalies can help the NICU RT anticipate and address specific respiratory needs.