Lack of utility of amniotic fluid index in predicting perinatal morbidity and mortality

Abstract

We read the article by Casey et al (Casey BM, McIntire DD, Bloom SL, Lucas MJ, Santos R, Twickler DM, et al. Pregnancy outcomes after antepartum diagnosis of oligohydramnios at or beyond 34 weeks’ gestation. Am J Obstet Gynecol 2000;182:909-12), who added additional patients to assist in understanding the significance of the ultrasonographic estimate of amniotic fluid volume. Their amniotic fluid index method is uncertain from this article. The reference quoted1Magann EF Chauhan SP Kinsella MJ McNamara MF Whitworth NS Morrison JC. Antenatal testing among 1001 patients at high risk: the role of ultrasonographic estimate of amniotic fluid volume.Am J Obstet Gynecol. 1999; 180: 1330-1336Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar does not address the presence of the cord in the vertical pocket of fluid. Did the multiple examiners measure to the cord or through the cord if only a single loop was present? With the interobserver and intraobserver variability and 6 years of examiners, if all examiners did not measure cord-containing pockets similarly, then the variation in measurements would be unacceptable. This study evaluated pregnancies complicated by size-date discrepancies, fetal growth, uncertain gestational age, possible anomalies, and other indications. It is difficult to extrapolate from these indications whether these patients were high-risk patients, normal-risk patients with growth irregularities or anomalies, or a combination of both. Have Casey et al concluded that both low- and high-risk pregnancies are at risk for increased perinatal morbidity and mortality if the amniotic fluid index is ≤ 5? The use of receiver operating characteristic curves would have helped to determine whether 5 is the threshold of an adverse outcome. Casey et al stated that 10% of the infants with oligohydramnios had major malformations. Congenital syndromes were also recognized in 20% of the infants with oligohydramnios. It is difficult to tell from the article whether the major malformations were included in the congenital syndromes. If they were, 1 of 5 of the infants with oligohydramnios had either major malformations or a congenital syndrome, or both. If the major malformations were not included in the congenital syndromes, then 1 of 3 of the infants with oligohydramnios had a major anomaly or a congenital syndrome. After Casey et al corrected for malformations, there was no difference between the group with normal ultrasonographic estimates of amniotic fluid volume and the group with oligohydramnios with respect to rates of cesarean delivery for fetal distress, cord umbilical artery pH ≤7, admission to the intensive care nursery, seizures in the first 24 hours after birth, or neonatal death. We disagree with the conclusions of Casey et al on the basis of their own data. Actually, Casey et al appear to have validated our conclusion1Magann EF Chauhan SP Kinsella MJ McNamara MF Whitworth NS Morrison JC. Antenatal testing among 1001 patients at high risk: the role of ultrasonographic estimate of amniotic fluid volume.Am J Obstet Gynecol. 1999; 180: 1330-1336Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar and the conclusions of others2Conway DL Adkins WB Schroeder B Langer O. Isolated oligohydramnios in the term pregnancy: is it a clinical entity?.J Matern Fetal Med. 1998; 7: 197-200Crossref PubMed Scopus (50) Google Scholar that the ultrasonographic estimation of oligohydramnios does not appear to be associated with increased perinatal morbidity and mortality relative to an ultrasonographic estimation of normal amniotic fluid volume after exclusion of malformations. 6/8/111090