What is the normal amniotic fluid index (AFI)?

RIMS Nursing Officer - 2022

Obstetrics & Gynaecology

Easy

Appeared in: RIMS Nursing Officer - 2022

Explanation

The normal Amniotic Fluid Index (AFI), a key indicator of fetal well-being, is defined as a value between 5 cm and 25 cm.
This range represents an adequate volume of amniotic fluid, which is essential for fetal lung development, movement, and protection against umbilical cord compression.
The AFI is determined by an ultrasound examination where the deepest, cord-free pocket of fluid is measured in each of the four quadrants of the uterus and the values are summed.

Option A: This range is too narrow. While an AFI of 5-10 cm is within the normal range, it incorrectly excludes the upper half of normal values (11-25 cm), potentially leading to misclassification of a healthy pregnancy as having borderline low fluid.
Option B: This range is also too restrictive. It omits the upper limit of the normal range, which extends to 24 or 25 cm. A pregnancy with an AFI of 22 cm is normal but would be incorrectly excluded by this option.
Option D: This range is too broad and is incorrect because it includes values that define polyhydramnios (excess amniotic fluid). An AFI greater than 24 or 25 cm is considered abnormal and is associated with increased risks.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Normal Amniotic Fluid Index (AFI) range as background academic context rather than a clinical decision trigger.
AFI measurement is a fundamental component of antenatal fetal surveillance, particularly in high-risk pregnancies or post-term pregnancies, to assess fetal well-being.
An abnormal AFI prompts further investigation. Oligohydramnios (AFI less than 5 cm) may suggest placental insufficiency or fetal renal problems and increases the risk of cord compression. Polyhydramnios (AFI greater than 25 cm) may be associated with maternal diabetes or fetal anomalies affecting swallowing.
Nursing interventions for oligohydramnios may include maternal hydration and increased fetal monitoring, while polyhydramnios may require monitoring for preterm labor and maternal respiratory symptoms.

How to Approach the Question

Identify the core concept being tested, which is the 'normal amniotic fluid index (AFI)'.
This is a factual recall question that requires knowledge of a standard reference value used in obstetrics.
Recall the definitions for normal AFI, oligohydramnios (too little fluid), and polyhydramnios (too much fluid).
The normal range is defined as being greater than 5 cm and less than 25 cm.
Compare this established range with the options provided.
Eliminate options that represent an incomplete range (5-10 cm, 5-20 cm) or an abnormally wide range that includes polyhydramnios (5-35 cm).

Concept Tested & Keywords

QDKtiBj2zPXZUw1keZuyDi

E6 Obstetrics Williams pp. 50-70, 49-70, 54-72