Amniotic Fluid Index (AFI) & Single Deepest Pocket

The AFI (Phelan technique) is the sum of the largest cord- and limb-free vertical pocket in each of the four uterine quadrants. Oligohydramnios is an AFI of 5 cm or less (some publications state below 5 cm) or a single deepest pocket below 2 cm. Polyhydramnios is an AFI at or above 24 cm (SMFM Consult #46; graded mild 24.0–29.9, moderate 30.0–34.9, severe ≥35 cm) or, under the traditional 95th–97th percentile convention, at or above 25 cm (mild 25–<30, moderate 30–<35, severe ≥35 cm); a single deepest pocket of 8 cm or more also defines polyhydramnios, graded mild 8–11 cm, moderate 12–15 cm, severe ≥16 cm per SMFM Consult #46. When the two methods disagree, both classifications are shown and the more abnormal one drives the headline.