Amniotic fluid plays a vital role in pregnancy, cushioning the baby, allowing movement, helping lung development, and maintaining a stable temperature. The Amniotic Fluid Index (AFI) is one method used by healthcare providers during an ultrasound to estimate the volume of this fluid.
How is AFI Measured?
During an ultrasound, the technician divides the uterus into four imaginary quadrants using the mother's navel (belly button) as the center point. In each quadrant, they measure the deepest vertical pocket of amniotic fluid (free of umbilical cord or fetal parts) in centimeters (cm). The AFI is simply the sum of these four measurements.
AFI (cm) = Quadrant 1 (cm) + Quadrant 2 (cm) + Quadrant 3 (cm) + Quadrant 4 (cm)
What Do the AFI Ranges Mean?
The calculated AFI is compared to standard reference ranges:
- Oligohydramnios (Low Fluid): Generally defined as AFI ≤ 5.0 cm. This requires investigation into the cause (e.g., ruptured membranes, placental issues, fetal kidney problems, post-term pregnancy) and close monitoring or intervention.
- Borderline Low: AFI between 5.1 cm and 8.0 cm. Management depends on gestational age and overall fetal well-being. May require increased monitoring.
- Normal: Typically AFI between 8.1 cm and 24.9 cm (though some sources use >5 to <24 or <25 cm). This generally indicates an adequate fluid volume.
- Polyhydramnios (High Fluid): Generally defined as AFI ≥ 25.0 cm (or sometimes >24 cm). Requires investigation into potential causes (e.g., maternal diabetes, fetal anomalies, multiple gestation, infections) and appropriate management.
Note: Sometimes a 'Single Deepest Pocket' (SDP) measurement is used instead of, or in addition to, AFI. Normal SDP is typically 2-8 cm.
Using This Calculator: Critical Limitations
This tool performs a simple calculation based on the numbers YOU provide from an ultrasound report.
- It requires accurate measurements from a medical ultrasound.
- It does NOT perform an ultrasound or measure fluid.
- Interpretation depends on gestational age and clinical context, which this calculator doesn't account for. Normal AFI ranges can vary slightly throughout pregnancy.
- It is NOT a substitute for professional medical evaluation.
Always Discuss with Your Provider
Your AFI is just one piece of information about your pregnancy health. Always discuss your ultrasound results, including the AFI measurement and its interpretation, directly with your doctor, midwife, or ultrasound technician. They will consider it alongside other factors like fetal growth, placental health, and your overall well-being to make clinical decisions.