Objective method of diagnosing oligohydramnios in postterm pregnancies.

Oligohydramnios is an important factor influencing the management of postterm pregnancies. However, sonographic assessment of oligohydramnios has been based largely on the subjective judgement of the sonologist. From January 1982 to December 1984, 54 patients had articulated-arm B-scan ultrasound examinations and were identified as postterm. Of these patients, 25 were subjectively diagnosed as having oligohydramnios. Five patients were considered to have low normal amounts of amniotic fluid. The remainder were considered to have normal or greater than normal quantities of amniotic fluid. From this population, an amniotic fluid index was determined for each patient by finding the product of the length, width, and depth of the largest amniotic fluid pocket. Patients with a fluid index less than 60 showed a strong association with the postmaturity syndrome. Indeed, all but one postmature infant was born of a pregnancy with a fluid index less than 60. No other fetal or perinatal complications were statistically correlated with oligohydramnios in this small patient series.