Amniotic fluid assessment. Methods and role in fetal assessment

AFV assessment by one method or another has become an adjunct to nonstress testing in most pregnancies requiring surveillance. Evaluation by nonstress test and amniotic fluid assessment for fetuses with maternal risk factors in a protocol such as that outlined by Devoe is common practice. Adaptation of that algorithm (Fig. 4) to the needs of the clinical setting are simple. Quantitative and nonquantitative methods show an increase in perinatal morbidity and mortality with abnormal values. Those trends are most evident in studies involving postdate gestations, such as those by Marks and Lagrew. The literature and its applied lessons for clinical practice are confused by the many variables considered by those investigating AFV assessment. Superiority of one method over another has not been demonstrated consistently from one study to the next. The good correlation in AFV estimated by ultrasonography and determined by dye-dilution techniques is still based on limited studies that are unlikely to be replicated soon because of the invasive nature of the test. Even in the best circumstances, errors at extremes of AFV are common with the use of ultrasonography. At present, the best recommendations from the literature seem to take two main directions. Antenatal testing of the fetus at risk should include some evaluation of AFV. The fetus with apparently abnormal AFV should be studied anatomically and considered for delivery if decreased AFV is associated with other test abnormalities--i.e., a nonreactive nonstress test.