Never Neglect the Amniotic Fluid Index in Prenatal Checkups — The Barometer of Fetal Health

Amniotic fluid is known as the life-sustaining liquid of pregnancy, serving as a protective cushion and nutritional supply for the fetus. Nutrients pass through the placenta, and fetal urine is the main source of amniotic fluid.

The Amniotic Fluid Index (AFI) is a core ultrasound indicator for measuring amniotic volume, reflecting the fetus's intrauterine condition and warning of hidden pregnancy risks.

Definition and Normal Range of AFI

AFI is calculated by summing the maximum vertical amniotic depth measured in four uterine quadrants via B-ultrasound, routinely tested after 28 weeks of gestation when amniotic volume is adequate.

Normal range: 8-25 cm; oligohydramnios (low fluid): below 5 cm; polyhydramnios (excess fluid): over 30 cm.

Why AFI Screening Matters

An abnormal AFI hints at fetal malformations or gestational complications, helping doctors arrange pregnancy management and delivery plans.

Polyhydramnios (AFI over 30 cm)

Causes: fetal neural tube or digestive tract defects, chromosomal anomalies; maternal gestational diabetes, hypertension, monozygotic multiple pregnancy.

• Mild polyhydramnios (25-30 cm): regular follow-up; limit sugar and water intake if the fetus is healthy.
• Severe polyhydramnios (over 35 cm) with chest tightness or dyspnea: amniocentesis drainage for symptom relief. Pregnancy termination may be considered for severe fetal deformity, based on gestational age and parental decision. Continuous fetal heart monitoring is required in labor to prevent premature membrane rupture and cord prolapse; a C-section is performed when necessary.

Oligohydramnios (AFI below 5 cm, higher risk)

Causes: fetal urinary system malformation, chromosome disorders; maternal dehydration, hypertension, placental insufficiency; premature rupture of membranes, post-term pregnancy over 42 weeks.

Mild low fluid (5-8 cm): increase oral fluids or use intravenous hydration, plus regular ultrasound review with a normal fetus.

Expectant mothers need not panic over an abnormal AFI. Regular prenatal visits help identify the root cause for personalized clinical management.