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Letter to the Editor |
Department of Ob/Gyn, Harbor-UCLA Medical Center, Torrance, California
To the Editor:
Magann et al1 suggest that the amniotic fluid index (AFI) offers no advantage over the single deepest pocket. In their randomized clinical trial, more patients in the AFI group were identified as oligohydramnios and had labor induced for this indication. An increased rate of cesarean delivery for fetal intolerance of labor was observed among all patients in the AFI assessment group (with and without oligohydramnios), although there was no difference between the AFI group and the single deepest pocket group among patients who actually had oligohydramnios. As the health care providers had no knowledge of whether AFI or single deepest pocket was utilized to define oligohydramnios, it is highly unlikely that either method contributed to the differential rate of cesarean delivery.
It is critical to recognize that screening criteria for oligohydramnios are not designed to identify a fetus who is presently at risk of intolerance to labor, but rather to prevent adverse clinical outcomes (eg, stillbirth, asphyxia) should the patient's labor not be induced. As all of the patients with identified oligohydramnios, by AFI or single deepest pocket, were induced in this study, one cannot determine the value of either the AFI or single deepest pocket in assessing the sequelae of discharge without delivery. As discussed by Moore,2 Morris et al3 utilized a study design in which results of AFI and single deepest pocket examinations were concealed and not utilized for patient management. It is only with the lack of intervention that one can determine whether oligohydramnios predicts subsequent morbidity. Oligohydramnios defined by the AFI was significantly associated with severe adverse outcome (relative risk 4.6). Conversely, single deepest pocket performed poorly at predicting cesarean delivery for fetal distress, neonatal unit admission, meconium, or low 5-minute Apgar. In fact, AFI had a 29% sensitivity for identification of subsequent birth asphyxia compared with 0% for single deepest pocket. Thus, the evidence indicates that, when patients are followed conservatively, a threshold AFI less than 5 cm will predict infants suffering asphyxia and/or meconium before the time point at which the single deepest pocket reveals oligohydramnios. The single deepest pocket less than 2 cm is far too stringent a criterion to be useful as a threshold for clinical intervention. A potential increase in labor inductions is of minimal consequence compared with the development of fetal asphyxia before labor. As such, evidence indicates that the AFI is markedly superior as a threshold for clinical intervention to the more stringent single deepest pocket and strongly supports the continued use of the AFI for amniotic fluid assessment.
doi:10.1097/01.AOG.0000151955.17500.a5
REFERENCES
1. Magann EF, Doherty DA, Field K, Chauhan SP, Muffley PE, Morrison JC. Biophysical profile with amniotic fluid volume assessments. Obstet Gynecol 2004;104:5–10.
2. Moore TR. Sonographic screening for oligohydramnios: does it decrease or increase morbidity? Obstet Gynecol 2004;104:3–4.
3. Morris JM, Thompson K, Smithey J, Gaffney G, Cooke I, Chamberlain P, et al. The usefulness of ultrasound assessment of amniotic fluid in predicting adverse outcome in prolonged pregnancy: a prospective blinded observational study. BJOG 2003;110:989–94.[Medline]
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