Determination of amniotic fluid volume in twin pregnancies: ultrasonographic evaluation versus operator estimation.

Abstract

We sought to determine the accuracy of amniotic fluid volume estimation (visually) in diamniotic twin pregnancy versus ultrasonography techniques. In this prospective study the volume of each sac in 23 sets of diamniotic twin pregnancies was subjectively and objectively estimated by a second-year obstetric resident, nurse sonographer, maternal-fetal medicine fellow, and maternal-fetal medicine staff. The actual volume was confirmed by amniocentesis and a dye-dilution technique. There was no difference in the total number of correct estimates of volume by level of operator experience (P =.98), ultrasonography technique (P =.87), or combined subjective versus objective correct estimates (P =.87). Identification of low volume was not different among the four evaluators (P =.48), but the percentage of correct estimates was poor (7%-29%). The 2-diameter pocket was a better predictor of oligohydramnios (57%) than the amniotic fluid index or the largest vertical pocket (12.5%; P =.002). The extremes of volume (low or high) are poorly identified by the subjective or objective assessment of volume.