What is the normal range (in mm) for the amniotic fluid index at 24 weeks of gestation?

Amniotic fluid is critically important for fetal growth. Abnormal amniotic fluid volume—particularly deviations from the standard amniotic fluid depth—can adversely affect the fetus. So, what is the normal range (in millimeters) for the amniotic fluid index (AFI) at 24 weeks of gestation?

What is the normal amniotic fluid index (AFI) range (in mm) at 24 weeks’ gestation?

At 24 weeks of pregnancy, the normal AFI range is 9–23 cm. Amniotic fluid protects the fetus from external mechanical forces and participates in fetal metabolism, while also safeguarding the mother and reducing discomfort caused by fetal movements. During ultrasound examination, the uterine cavity is divided into four quadrants: upper left, upper right, lower left, and lower right. The AFI is calculated as the sum of the maximum vertical depths (in centimeters) of the deepest amniotic fluid pockets in each of these four quadrants. An AFI exceeding 24 cm indicates polyhydramnios (excessive amniotic fluid); an AFI between 18 cm and 24 cm suggests possible or borderline polyhydramnios.

Amniotic fluid provides cushioning and protective functions for the fetus—for instance, when the maternal abdomen sustains external trauma, the fetus is not directly injured due to this protective buffer. Additionally, amniotic fluid acts as a lubricant, and fetal growth and development depend on it. Within the uterus, the fetus performs swallowing movements, ingesting amniotic fluid. This process is vital for the development of the fetal digestive and respiratory systems.

In early pregnancy, oligohydramnios (low amniotic fluid volume) or anhydramnios (absence of amniotic fluid) may lead to bronchopulmonary dysplasia in the fetus. Furthermore, when no amniotic fluid is present, the amniotic membrane may adhere directly to the fetal body surface, potentially resulting in amniotic band syndrome and consequent fetal developmental abnormalities. We hope this information is helpful to you. Wishing you good health and happiness!