Amniotic Fluid Index (AFI) Test: When Should You Worry?

The amniotic fluid index test in pregnancy measures the amount of fluid around your baby and helps doctors monitor fetal wellbeing.

Pregnancy ultrasounds do much more than reveal your baby’s profile or estimate growth.

One important measurement routinely assessed during pregnancy is the Amniotic Fluid Index (AFI).

If your healthcare provider has mentioned that your AFI is “low,” “borderline,” or “higher than expected,” you may understandably feel anxious.

Questions such as:

“What exactly is the AFI test?”

“What does my AFI number mean?”

“Can abnormal fluid levels affect my baby?”

are extremely common.

As a women’s health physiotherapist, I frequently meet expectant mothers who become worried after hearing terms like oligohydramnios or polyhydramnios.

Fortunately, in many situations, AFI measurements simply help healthcare providers monitor pregnancy more closely and ensure that both mother and baby remain healthy.

Understanding the AFI test can make conversations with your healthcare provider much less stressful.

What Is Amniotic Fluid?

Amniotic fluid is the clear, protective liquid that surrounds your baby inside the uterus.

This remarkable fluid performs several important functions throughout pregnancy.

It:

• Cushions the baby against injury.
• Allows free movement and growth.
• Supports lung development.
• Helps maintain a stable temperature.
• Prevents compression of the umbilical cord.
• Reduces the risk of infection.

Amniotic fluid is produced by both maternal and fetal sources during early pregnancy, while fetal urine becomes the major contributor later in pregnancy.

According to the Mayo Clinic low amniotic fluid guide, amniotic fluid volume often reflects overall fetal and placental health.

What Is the Amniotic Fluid Index (AFI) Test?

The AFI test is an ultrasound-based measurement used to estimate the volume of amniotic fluid inside the uterus.

It is one of the most widely used methods for assessing amniotic fluid volume during pregnancy.

Healthcare providers commonly perform AFI measurements during:

• Routine third-trimester scans.
• Growth scans.
• Biophysical Profile (BPP) assessments.
• High-risk pregnancy monitoring.
• Evaluation of reduced fetal movements.

The American College of Obstetricians and Gynecologists (ACOG) guidance on antenatal fetal surveillance identifies amniotic fluid assessment as an important component of fetal surveillance in selected pregnancies.

How Is the AFI Measured?

The AFI test is performed during a standard abdominal ultrasound.

The uterus is divided into four imaginary sections or quadrants.

The sonographer measures the deepest pocket of fluid in each quadrant and then adds these measurements together.

The final sum is called the Amniotic Fluid Index.

The procedure is:

• Painless.
• Non-invasive.
• Safe during pregnancy.
• Usually completed within a few minutes.

Research by Phelan on AFI measurement standards established the four-quadrant technique that continues to be widely used in clinical practice.

When Is an AFI Test Performed?

An AFI assessment may be performed whenever healthcare providers need additional information regarding fetal well-being.

Common reasons include:

High-Risk Pregnancy

Women with certain medical conditions may require additional surveillance.

Examples include:

• Gestational diabetes.
• Chronic hypertension.
• Preeclampsia.
• Kidney disease.
• Autoimmune disorders.

Suspected Fetal Growth Restriction

Babies who appear smaller than expected often undergo AFI assessment.

Reduced Fetal Movements

Changes in fetal movements frequently prompt ultrasound evaluation, including AFI measurement.

Post-Term Pregnancy

Pregnancies continuing beyond the due date often require additional fetal surveillance.

Multiple Pregnancy

Twin and higher-order pregnancies may require closer monitoring.

What Is Considered a Normal AFI?

Although values vary slightly across guidelines, a normal AFI in singleton pregnancies generally ranges from 5 to 24 cm.

AFI Measurement	Interpretation
5-24 cm	Normal range
5 cm or less	Oligohydramnios (low fluid)
24 cm or greater	Polyhydramnios (excess fluid)

According to Crellin and colleagues in the updated StatPearls review on sonographic evaluation of amniotic fluid, an AFI of 5 to 24 cm is generally considered normal in singleton pregnancies (Crellin et al. 2025)

What Is Oligohydramnios?

Oligohydramnios means that the amount of amniotic fluid is lower than expected for the stage of pregnancy.

It is typically diagnosed when:

• AFI is 5 cm or less, or
• The single deepest pocket measures less than 2 cm.

Possible causes include:

• Placental insufficiency.
• Rupture of membranes.
• Maternal hypertension.
• Fetal kidney abnormalities.
• Post-term pregnancy.
• Certain medications.

Oligohydramnios has been associated with increased risks of pregnancy complications and usually requires closer fetal surveillance (Bynarowicz et al. 2025)

The Mayo Clinic overview on low amniotic fluid also notes that low fluid levels can occasionally indicate placental problems or fetal conditions.

What Is Polyhydramnios?

Polyhydramnios refers to excessive amniotic fluid.

It is commonly diagnosed when:

• AFI is 24 cm or greater, or
• The deepest fluid pocket measures 8 cm or greater.

Potential causes include:

• Maternal diabetes.
• Fetal swallowing disorders.
• Fetal anomalies.
• Twin-to-twin transfusion syndrome.
• Unknown causes (idiopathic polyhydramnios).

Fortunately, many mild cases have no identifiable cause and result in healthy pregnancies.

According to (Hwang et al. 2024), the Society for Maternal-Fetal Medicine recommends defining polyhydramnios as an AFI of 24 cm or greater

The Mayo Clinic polyhydramnios overview reports that polyhydramnios affects approximately 1% to 2% of pregnancies.

Symptoms That May Suggest Abnormal Amniotic Fluid Levels

Many women experience no symptoms.

However, possible symptoms include:

Symptoms of Low Amniotic Fluid

• Reduced fetal movements.
• Leaking fluid from the vagina.
• Smaller-than-expected abdominal growth.

Symptoms of Excess Amniotic Fluid

• Rapid abdominal enlargement.
• Breathlessness.
• Abdominal discomfort.
• Swelling.
• Difficulty lying flat.

Remember that symptoms alone cannot diagnose abnormal fluid levels. Ultrasound assessment is always required.

A Physiotherapist’s Perspective: Why AFI Matters

As a women’s health physiotherapist, I often remind expectant mothers that AFI measurements are just one piece of the overall pregnancy picture.

An isolated borderline AFI value does not automatically mean something is wrong.

Healthcare providers always interpret AFI findings alongside:

• Fetal growth.
• Doppler studies.
• Maternal symptoms.
• Fetal movements.
• Other fetal surveillance tests.

Most women with borderline or mildly abnormal AFI measurements go on to have healthy pregnancies with appropriate monitoring and follow-up.

What Happens If Your AFI Is Abnormal?

Hearing that your amniotic fluid level is outside the normal range can be worrying.

However, an abnormal AFI result does not automatically mean that your baby is in danger.

Instead, it usually means that your healthcare provider wants to monitor the pregnancy more closely.

Management depends on several factors, including:

• Gestational age.
• Severity of the fluid abnormality.
• Fetal growth.
• Doppler ultrasound findings.
• Maternal symptoms.
• Underlying medical conditions.

Your healthcare provider will interpret AFI findings alongside the overall clinical picture rather than relying on a single measurement.

How Is Low Amniotic Fluid Managed?

Management of oligohydramnios depends on the underlying cause and the stage of pregnancy.

Possible management strategies include:

Increased Monitoring

Additional surveillance may include:

• Repeat AFI measurements.
• Growth ultrasounds.
• Doppler studies.
• Non-Stress Tests (NSTs).
• Biophysical Profiles (BPPs).

Maternal Hydration

Some studies suggest that maternal hydration may temporarily improve amniotic fluid levels in selected cases.

A systematic review by Hofmeyr GJ et al. found that maternal hydration can increase amniotic fluid volume in some pregnancies (Hofmeyr et al. 2002).

Treatment of Underlying Conditions

Management may involve treating:

• High blood pressure.
• Diabetes.
• Ruptured membranes.
• Placental insufficiency.

Delivery

In some situations, particularly near term, early delivery may be recommended if fetal well-being is a concern.

How Is Polyhydramnios Managed?

Treatment depends on:

• The severity of polyhydramnios.
• Maternal symptoms.
• Gestational age.
• The presence of fetal abnormalities.

Mild cases often require only observation and regular follow-up.

Management may include:

• Serial ultrasound scans.
• Blood sugar assessment for diabetes.
• Additional fetal surveillance.
• Monitoring for preterm labour symptoms.

Severe cases may occasionally require specialised treatment.

According to Hwang DS et al., mild idiopathic polyhydramnios is associated with favourable outcomes in most pregnancies, although additional surveillance may still be recommended (Hwang DS et al., 2024)

AFI vs Single Deepest Pocket: What Is the Difference?

Healthcare providers use two main methods to assess amniotic fluid volume.

Amniotic Fluid Index (AFI)

AFI measures the deepest fluid pocket in each of four uterine quadrants and adds them together.

Single Deepest Pocket (SDP)

The SDP technique measures only the largest vertical pocket of fluid.

Many professional organisations increasingly prefer the SDP method because it may reduce unnecessary interventions.

A Cochrane review by Nabhan AF and Abdelmoula YA found that using the single deepest pocket method instead of AFI may reduce unnecessary obstetric interventions without compromising pregnancy outcomes (Nabhan et al. 2008)

Can AFI Change During Pregnancy?

Yes.

Amniotic fluid volume changes continuously throughout pregnancy.

Fluid levels generally:

• Increase steadily during early pregnancy.
• Peak around the early third trimester.
• Gradually decrease toward the due date.

AFI can also fluctuate over short periods.

Factors influencing fluid levels include:

• Maternal hydration status.
• Placental function.
• Fetal urination.
• Rupture of membranes.
• Maternal medical conditions.

For this reason, healthcare providers sometimes repeat AFI measurements before making major clinical decisions.

Is the AFI Test Safe?

Yes.

The AFI test uses standard diagnostic ultrasound, which is considered safe during pregnancy when performed by trained healthcare professionals.

A World Health Organization systematic review found no evidence that medically indicated diagnostic ultrasound causes adverse maternal or fetal outcomes (Torloni et al. 2009).

The examination:

• Does not expose the mother or baby to radiation.
• Is painless.
• Is non-invasive.
• Can be repeated when clinically necessary.

Limitations of the AFI Test

Although AFI is widely used, it has limitations.

The test cannot:

• Guarantee a complication-free pregnancy.
• Predict labour onset.
• Identify every fetal problem.
• Determine long-term developmental outcomes.

Measurement differences between sonographers can occasionally occur.

AFI findings should always be interpreted alongside:

• Fetal growth assessment.
• Doppler studies.
• Maternal symptoms.
• Fetal movement patterns.
• Other fetal surveillance findings.

Questions You May Want to Ask Your Doctor

Consider asking:

• Is my AFI within the normal range?
• Will I need repeat ultrasounds?
• Do I require additional fetal monitoring?
• Could my AFI affect my birth plan?
• Should I monitor fetal movements more closely?
• What symptoms should prompt urgent medical review?

Preparing questions in advance can help you feel more informed and reassured.

Conclusion

The Amniotic Fluid Index is an important ultrasound assessment that helps healthcare providers evaluate fetal well-being during pregnancy.

Although hearing that your fluid levels are outside the normal range can be concerning, an abnormal AFI result does not automatically indicate a serious problem.

With modern fetal surveillance techniques and appropriate follow-up, most pregnancies affected by abnormal amniotic fluid levels can be managed successfully.

As a women’s health physiotherapist,

I encourage expectant mothers to attend all antenatal appointments, remain aware of fetal movements, and discuss any concerns openly with their healthcare provider.

Frequently Asked Questions (FAQs)

1. What is a normal AFI during pregnancy?

In singleton pregnancies, an AFI between approximately 5 and 24 cm is generally considered normal, although interpretation may vary slightly depending on gestational age and clinical guidelines.

2. Is the AFI test safe during pregnancy?

Yes. The AFI test uses standard diagnostic ultrasound and is considered safe when performed by trained healthcare professionals.

3. What causes low amniotic fluid?

Low amniotic fluid may occur due to placental insufficiency, rupture of membranes, maternal hypertension, fetal kidney problems, certain medications, or post-term pregnancy.

4. Can AFI levels change during pregnancy?

Yes. Amniotic fluid levels naturally change throughout pregnancy and may fluctuate due to hydration status, placental function, and fetal health.

5. What happens if my AFI is low?

Your healthcare provider may recommend additional monitoring, repeat ultrasounds, Doppler studies, NSTs, or delivery if clinically necessary.

6. Does an abnormal AFI always mean there is a problem with my baby?

No. Many women with mildly abnormal AFI measurements go on to have healthy pregnancies. AFI results are always interpreted alongside other clinical findings.

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Medical Disclaimer!

This article has been reviewed and written under the guidance of our Head Physiotherapist, Dr. Kruti Raj (PT, MUHS,CPT,CMPT). The information shared is intended for educational purposes only and should not be considered a substitute for personalized medical advice, diagnosis, or treatment.

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