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

OBJECTIVE: We sought to determine the accuracy of amniotic fluid volume est imation (visually) in diamniotic twin pregnancy versus ultrasonography tech niques. STUDY DESIGN: In this prospective study the volume of each sac in 23 sets o f diamniotic twin pregnancies was subjectively and objectively estimated by a second-year obstetric resident, nurse sonographer, maternal-fetal medici ne fellow, and maternal-fetal medicine staff. The actual volume was confirm ed by amniocentesis and a dye-dilution technique. RESULTS: There was no difference in the total number of correct estimates o f volume by level of operator experience (P = .98), ultrasonography techniq ue (P = .87), or combined subjective versus objective correct estimates (P = .87). identification of low volume was not different among the four evalu ators (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). CONCLUSION: The extremes of volume (low or high) are poorly identified by t he subjective or objective assessment of volume.