The liquor volume is a good indicator of fetal wellbeing and growth-retardation.
The vertical diameter of 8 cm and 1 cm of any liquor pocket have been used to denote polyhydramnios and oligohydramnios. The perinatal mortality has been reported to be exceed 150/1000 livebirths in diameters <1cm.
More recently the Amniotic fluid index (AFI) is replacing the vertical diameter in the documenting liquor volume. The four- quadrant technique is used.
In this technique the transducer should be perpendicular to the floor. The sum of the largest vertical pockets in the 4 quadrants is normally 13 + 5cm*. 24 cm is used (+2sd) as the lower limit of normal for the diagnosis of polyhydramnios. This produced better correlation with fetal outcome than using a single pocket of 8 cm. A value below 5 cm is used to diagnose significant oligohydramnios after 16 weeks.
*Phelan JP; Ahn MO; Smith CV; Rutherford SE; Anderson E : Amniotic fluid index measurements during pregnancy. J Reprod Med, 1987 Aug, 32:8, 601-4