Limitations of using maximum vertical pocket and other sonographic evaluations of amniotic fluid volume to predict fetal growth: technical or physiologic?

Maximum vertical pocket measurement and subjective sonographic impression of amniotic fluid volume were studied in 487 selected pregnancies. Opiate abuse, suspected fetal growth retardation, and suspected postterm gestation were negatively correlated with maximum vertical pocket; suspected fetal growth acceleration and increasing birth weight were positively correlated. Maximum vertical pocket appeared to peak at 31 to 33 weeks (p less than 0.05), and was related to fetal growth (p less than 0.001). Subjective sonographic evaluation of amniotic fluid volume yielded comparable results. Unfortunately, neither technique could be used to accurately predict the birth of a small, appropriate, or large for gestational age infant in the individual pregnancy. Abnormal fetal growth could be reliably excluded in only a small number of cases. This and previous studies suggest that diagnosis of abnormal fetal growth by means of sonographic amniotic fluid volume evaluation could be limited by physiologic variation rather than technical error in measurement.