American Journal of Obstetrics and Gynecology (2004) 191, 661e8

www.elsevier.com/locate/ajog

Amniotic fluid index vs single deepest pocket techniqueduring modified biophysical profile: A randomizedclinical trial

Suneet P. Chauhan, MD,a,* Dorota D. Doherty, PhD,b Everett F. Magann, MD,c

Francis Cahanding, RN,d Frank Moreno, MD,d Jack H. Klausen, MDd

Spartanburg Regional Medical Center, Spartanburg, SCa; Department of Obstetrics and Gynecology, University ofWestern Australia, Perth, Australiab; Department of Obstetrics and Gynecology, Portsmouth Naval Hospital,Portsmouth, Vac; and Naval Hospital Camp Pendleton, Camp Pendleton, Calif d

Received for publication April 13, 2004; revised May 26, 2004; accepted June 18, 2004

KEY WORDSModified biophysical

profile

Amniotic fluid

Oligohydramnios

Objective: The purpose of this study was to determine the superior technique, if either, of the

amniotic fluid index (AFI) vs the single deepest pocket technique in predicting an adverse

pregnancy outcome among high-risk patients undergoing antenatal testing.

Study design: Patients having modified biophysical profile (nonstress test plus sonographic

estimation of amniotic fluid) were randomized to either have AFI or determination of the

presence or absence of a 2!1-cm single deepest pocket.

Results: Between January of 1997 and December of 2001, 1080 women were randomized with

530 women in the AFI arm, and 558 in the 2!1 pocket arm. The maternal demographics and

prenatal complications were similar between groups. Significantly more patients were identified as

having oligohydramnios using AFI (17%) compared with using 2!1 pocket (10%) (P = .002).

The overall rate of cesarean section for nonreassuring fetal heart rate (FHR) tracing was 3.8% (30

cases, with 16 cases in the AFI-monitored, and 14 cases in the 2!1 pocketemonitored groups,

respectively, P = .608). Logistic regression analysis showed no difference between the groups

with respect to the ability to identify patients who underwent cesarean section for nonreassuring

FHR tracing during labor (P = .999). The umbilical artery pH !7.1 (P = .688) and admission

to the newborn intensive care unit were also comparable between groups.

Conclusion: During antepartum fetal surveillance, use of single deepest pocket compared with

amniotic fluid index is associated with a significantly lower rate of suspected oligohydramnios.

� 2004 Elsevier Inc. All rights reserved.

Presented at the Sixty-Sixth Annual Meeting of the South Atlantic

Association of Obstetricians and Gynecologists, Boca Raton, Florida,

January 18-21, 2004.

* Reprint requests: Suneet P. Chauhan, MD, Division of Maternal-

Fetal Medicine, Regional Women’s Health Care, 853 N Church St,

Suite, Spartanburg, SC 29303.

E-mail: schauhan@srhs.com

0002-9378/$ - see front matter � 2004 Elsevier Inc. All rights reserved.

doi:10.1016/j.ajog.2004.06.078

Pregnancies at risk for adverse outcomes are man-aged with modified biophysical profile (BPP) thatconsists of a nonstress test and sonographic evaluationof amniotic fluid. Antenatal assessment of amniotic fluidis important because it reflects long-term uteroplacentalfunction, and aberrations of this volume have been

662 Chauhan et al

associated with adverse outcomes.1 Oligohydramnios,for example, is linked with genitourinary anomalies,postural deformities, nonreassuring fetal heart rate(FHR) tracing, and an increased risk of perinatalmorbidity and death.2,3 Presently, the 2 techniques toensure adequacy of amniotic fluid include amniotic fluidindex (AFI), which is the summation of the largestvertical pocket in 4 quadrants, and the single deepestpocket technique. According to these 2 estimates ofamniotic fluid volume, an AFI %5.0 cm,4 or the absenceof a single deepest pocket of at least 2!1 cm isdiagnostic of oligohydramnios.5 The AFI is increasinglyused in the modified BPP, despite the fact that the idealcutoff for intervention has not been clearly established.There are conflicting reports about the ability of index% vs O5.0 cm to identify adverse peripartum out-comes,3,6-10 and a paucity of randomized clinical trials.

A PubMed search for randomized clinical trials inEnglish with terms ‘‘modified biophysical profile, amni-otic fluid index’’ found 3 publications,11-13 and only oneof them allocated patients to 1 of the 2 methods ofassessing amniotic fluid. Alfirevic et al11 randomizedpost-term pregnancies (at least 290 days) to AFI andsingle deepest pocket, and noted the use of AFI wasassociated with a significantly higher rate of inductionwithout an improvement in perinatal outcomes. Becausethis publication was limited to postdate pregnancies,and used gestational ageebased criteria for oligohy-dramnios, we wanted to determine if the findings wereapplicable to all high-risk pregnancies1 that underwentmodified BPP testing.

The purpose of this randomized clinical trial was todetermine the impact, if any, of using the AFI comparedwith the single deepest pocket in conjunction witha nonstress test among high-risk pregnancies.

Material and methods

This prospective clinical trial was approved by theClinical Investigation Division at the Naval MedicalCenter, San Diego, Calif, which is the InstitutionalReview Board for Naval Hospital Camp Pendleton, andthe Investigational Review Board at the University ofMississippi Medical Center. All consecutive high-riskpatients undergoing serial fetal surveillance were ap-proached to participate in the prospective, randomized,clinical trial. The inclusion criteria were medical orobstetric problems complicating pregnancy and beingmanaged with weekly modified BPP. The patients wereexcluded if they had multiple gestations, known fetalanomalies, or refused study participation. If they agreedto take part in the study, an opaque sealed envelope wasopened, and the patient was assigned to have theamniotic fluid assessed either with AFI or single deepestpocket.

As described by Phelan et al, 4 the AFI was obtainedby dividing the abdomen in 4 quadrants, obtaining thedeepest pocket in each quadrant and summing them up.Patients assigned to the single deepest pocket wereevaluated according to Chamberlain et al.14 Oligohy-dramnios defined as AFI%5.0 cm, or absence of a singledeepest pocket of 2!1 cm was an indication for deliveryif the gestational age was 34 weeks or more. Oncea patient was assigned to AFI or single deepest pocketarm, all subsequent assessments of amniotic fluid weredone accordingly. Clinicians managing the patients wereaware of the results of the modified BPP, and whetherAFI or single deepest pocket was used to evaluate theamniotic fluid. The amniotic fluid estimation, AFI orsingle deepest pocket, used for this evaluation is the lastvolume estimated before delivery. In pregnancies com-plicated by diabetes or intrauterine growth restrictionthe last amniotic fluid estimation would have beenwithin 3 days of delivery, and in all other pregnancieswithin 7 days of delivery.

All cesarean deliveries were done by obstetrics andgynecology residents under the supervision of an at-tending. Cesarean delivery for cephalopelvic dispropor-tion was done according to the American College ofGynecology guidelines,15 and they were done for non-reassuring FHR tracing if the abnormality did notrespond to intrauterine resuscitative efforts like hydra-tion, position change, oxygenation, amnioinfusion, andterbutaline, where applicable.16 At delivery, the umbil-ical cord was doubly clamped, and an arterial bloodsample was obtained in a preheparinized syringe. Thesample was placed on ice and analyzed (Corning 178analyzer, Medfield, Mass) within 30 minutes of thedelivery.

Randomization was accomplished via use of a com-puter-generated random number table with blockedpermutations. Randomization was accomplished byopening sealed opaque envelopes containing groupallocations that were prepared in blocks of 14 envelopes,7 per allocation. When the envelope pack was reducedto 8 envelopes, a new block of 14 envelopes wassupplemented. A person not directly associated withthe study performed randomization and envelope prep-aration. The primary end point of the analysis was theincidence of cesarean section for nonreassuring FHRtracing. Sample size calculations indicated that a sampleof 1080 women would achieve 80% power in detectinga difference of 5% vs 9% in the rate of cesarean sectionfor nonreassuring FHR tracing between treatment armsusing a chi-square test at 5% significance level.

Descriptive statistics used means and standard devia-tions or medians and interquartile ranges (Q1-Q3) andpercentages, as appropriate for continuous and categor-ical data. Performance of AFI and 2!1 pocket moni-toring was also evaluated by their sensitivity (proportionof cases with adverse outcome identified with either AFI

Chauhan et al 663

or 2!1 pocket monitoring) and specificity (proportionof normal outcomes as identified with normal amnioticfluid volume using either AFI or 2!1 pocket monitor-ing) to identify women likely to experience adverseoutcomes.

The primary end point and other categorical out-comes were investigated using chi-square tests. Allsubjects were analyzed on an ‘‘intent to treat’’ basis.Supplementary analyses included logistics regressionmodeling to investigate factors associated with eachoutcome considered (incidence of nonreassuring FHRtracing, cesarean section for nonreassuring FHR trac-ing, and admission to neonatal intensive care nursery).In logistic regression models, an interaction of mode ofmanagement (AFI vs 2!1 pocket) and ‘high-risk’ status(defined as AFI %5.0 cm or 2!1 pocket not present)was investigated in combination to assess whether oneof these indices was more predictive of adverse outcome.Along with sensitivity and specificity, likelihood ratios(LR = sensitivity over 1- specificity) for positive (oligo-hydramnios) and negative (adequate amniotic fluid)tests were calculated for each group. According to theguidelines established by the Evidence-Based MedicineWorking Group,17 a diagnostic test may be categorizedas definitively useful if LR O10 or !0.1, moderatelyuseful if LR 5 to 10 or 0.1 to 0.2, slightly useful if LR 2to 5 or 0.2 to 0.5, and not useful LR 1 to 2 or 0.5 to 1.Statistical analysis was conducted using SPSS statisticalsoftware (SPSS version 11.0, Inc, Chicago, Ill). Logisticregression analyses were carried out using LogXactlogistic regression software (Cytel version 5, Cambridge,Mass). P values ! .05 were considered statisticallysignificant.

Results

One thousand eighty women were randomized into 1 ofthe 2 management regimens, using either AFI or 2!1pocket assessment antenatally. Five hundred fifty-eightwomen were managed with the 2!1 pocket, and 530patients were monitored with the AFI. Maternal de-mographics were similar between the groups (Table I).Peripartum outcomes are summarized in Table II. Therewas a considerable difference between the ‘high-risk’status as defined by AFI %5.0 cm compared with the‘high-risk’ status assigned due to the absence of 2!1pocket (88 patients [17%] vs 57 patients [10%]). Withinthe preterm deliveries (gestational age !37 weeks), 19%(9 cases) had oligohydramnios in the AFI monitoredgroup and 11% (6 cases) in the 2!1 pocket group(P = .401).

There were no differences between the rates of vari-able decelerations present (P = .662); moreover, therewere no differences in variable decelerations influencingdelivery among the patients where variable decelerations

were observed (P = .279). There were differences be-tween the rates of minimal or absent variability presentbetween the groups (P = .046). Late decelerations weresimilar between the groups (P = .133), and the rates ofabnormal decelerations influencing delivery were alsoalike (P = .279).

Mode of delivery and reasons for operative deliverywere alike (Table II). The rate of nonreassuring FHRtracing was similar between the groups (P = .390), andlogistic regression analysis showed no difference be-tween the groups with respect to the ability of thesonographic estimation of amniotic fluid to identifypatients with nonreassuring FHR tracing during labor(P = .731). The overall rate of cesarean section fornonreassuring FHR tracing was 3.8% (30 cases with16 cases in the AFI-monitored, and 14 in the 2!1pocketemonitored groups, P = .608), and thesecesarean sections comprised 43% of all sections in theAFI-monitored group (out of 37 cesarean deliveries)and 38% of all cesarean sections in the2!1-monitored group (out of 37 c/s) (P = .637).Logistic regression analysis showed no differencebetween the groups with respect to the ability to identifypatients who underwent cesarean section for nonreassuringFHR tracing during labor (P = .999).

There were no differences between the groups formost of the neonatal outcomes (Table III). There was nodifference in the rate of admission to the newborn ICU

Table I Maternal characteristics stratified by mode ofmonitoring, AFI and 2!1 pocket

Group

Characteristic AFI (n = 530) 2!1 (n = 558) P value

Maternal age 24 (IQ 21-30) 25 (IQ 21-29) 0.396RaceCaucasian 317 (60%) 337 (60%)African American 104 (20%) 104 (19%)Others 109 (20%) 116 (21%) 0.924

Primigravida 185 (35%) 202 (36%) 0.656Nulliparous 265 (50%) 281 (50%) 0.906Prenatal complicationsHypertension 64 (12%) 63 (11%)Diabetes 68 (13%) 67 (12%)IUGR 39 (7%) 42 (8%)Raised MSAFP 66 (13%) 92 (17%)Post dates 204 (39%) 210 (38%)Oligohydramnios 13 (3%) 8 (1%)Other 76 (14%) 76 (14%) 0.548

Gestational ageat delivery

40 (IQ 38-41) 40 (IQ 38-41) 0.561

Gestational agedistribution

!37 47 (9%) 53 (10%)37-40 264 (50%) 279 (50%)Op40 219 (41%) 226 (41%) 0.921

664 Chauhan et al

Table II Peripartum outcomes stratified by sonographic assessment of AF volume, using either AFI or 2!1 pocket

Group

Characteristic AFI (n = 530) 2!1 (n = 558) P value

Oligohydramnios* 88 (17%) 57 (10%) 0.002Amnioinfusion 56 (11%) 44 (8%) 0.126Nonreassuring fetal heart rate (FHR) tracingy 34 (63%) 21 (48%) 0.155

Nonreactive NST 44 (8%) 51 (9%) 0.668Variable decelerationsPresent 77 (15%) 75 (13%) 0.662Infl deliveryy 67 (87%) 60 (80%) 0.279

VariabilityMin/absent 41 (8%) 63 (11%) 0.046

Late decelerationsPresent 37 (7%) 27 (5%) 0.133Infl deliveryy 33 (94%) 26 (96%) 0.999

Non-reassuring fetal heart rate (FHR) tracing 87 (16%) 83 (15%) 0.390Delivery modeSpont. Vaginal 365 (69%) 405 (73%)Assist. Vaginal 128 (24%) 116 (21%)Cesarean 37 (7%) 37 (7%) 0.377

Reason for cesarean deliveryy

Nonreassuring fetal heart rate (FHR) tracing 16 (43%) 14 (38%)Failure to progress 7 (19%) 14 (38%)Other 13 (35%) 9 (24%) 0.766

Reason for assisted vaginal deliveryy,z

Nonreassuring fetal heart rate (FHR) tracing 71 (56%) 69 (60%)Failure to progress 44 (34%) 35 (30%)Other 13 (10%) 11 (10%) 0.213

* AFI %5.0 cm in the AFI-monitored group, or 2!1 pocket not present in the 2!1 group, on the intrapartum AF assessment.y Percentages for subsets of patients with condition present are shown. One case of missing information about reason for cesarean delivery in

AFI-monitored group, and one case of missing reason for assisted vaginal delivery in the 2!1 pocketemonitored group.z Three cases of nonreassuring fetal heart rate (FHR) tracing noted in spontaneous deliveries (2 in AFI-monitored group and 1 in the 2!1 pocket

group).

(P= .328), but among the neonates admitted to thenewborn ICU there was a higher proportion of admis-sion for respiratory distress in the AFI-monitored group(P= .028). Among the preterm delivery, the rate ofrespiratory distress syndrome (RDS) was significantlyhigher among those randomized to the AFI (0.1%;6/530) than to 2!1 pocket (0%; P= .009). These 6premature deliveries were results of hypertensive disease(n = 2), preterm labor refractory to treatment withtocolytics (n = 3), and one case of fetal growth re-striction and oligohydramnios (AFI of 4.0 cm) at 34weeks. This last case was induced for abnormal growthand inadequate amniotic fluid, and had an uncompli-cated intrapartum course with a vaginal delivery ofa newborn weighing 1950 g, Apgar score of 5 at 5minutes, and umbilical arterial pH of 7.20. Thus, therate of iatrogenic prematurity due to the use of AFI was2% (1/47; 95% CI 0.05e11). There were no cases ofstillbirths in either group.

The predictive accuracies of the 2 methods of assess-ing amniotic fluid are provided in Table IV. Both AFIand 2!1 monitoring methods were characterized by low

sensitivity to identify women likely to experience adverseoutcomes with relatively high ability to predict normaloutcomes. Use of likelihood ratios and guidelines pro-vided by the Evidence-Based Medicine WorkingGroup17 indicates that both methods of evaluatingamniotic fluid are poor diagnostic tests in identifyingpatients that will undergo cesarean delivery for non-reassuring FHR tracing or deliver a newborn withdepression or acidosis.

Comment

The results of this randomized clinical trial are notablefor 3 major findings. First, during modified BPP, use ofthe AFI rather than single deepest pocket to estimate theamniotic fluid volume increases the likelihood of in-tervention without a demonstrable benefit. High-riskpatients were significantly more likely to be diagnosed ashaving oligohydramnios, be induced for an abnormalfluid volume, and undergo amnioinfusion if AFI is usedfor fetal assessment than the measurement of the largest

Chauhan et al 665

Table III Neonatal characteristics stratified by mode of monitoring, AFI and 2!1 pocket

Group

Characteristic AFI (n = 530) 2!1 (n = 558) P value

Birth weight 3490 (3074-3856) 3250 (3105-3830) 0.780Birth weight distribution!1500 1 (0.2%) 1 (0.2%)1500-2500 25 (5%) 25 (5%)2500-4000 414 (78%) 448 (80%)O4000 90 (17%) 84 (15%) 0.843

MeconiumPresent 65 (12%) 64 (12%) 0.685Thicky 39 (60%) 45 (70%) 0. 269

Umb artery pH !7.1* 14 (3%) 17 (3%) 0.688Apgar score !7 68 (13%) 67 (12%) 0.6811 min 12 (2%) 6 (1%) 0.1245 min

Admission to NICU 35 (7%) 29 (5%) 0.328Admission reasonsy 27 (82%) 15 (56%) 0.419RDS/TTN 4 (12%) 11 (41%)Sepsis 2 (6%) 1 (4%) 0.028Other

* There were 2 cases (ie, 0.4%) of pH !7.00 in each group.

y Percentages for subsets of patients with condition present are shown.

Table IV The predictive accuracies of adverse outcomes using amniotic fluid index or the presence/absence of a 2!1 pocket

AFI (n = 530) 2!1 (n = 558)

Sens Spec PPV NPV LR (C) LR (�) Sens Spec PPV NPV LR (C) LR (�)

CD for distress 6.3% 83.1% 0.8% 96.6% 0.4 0.9 7.7% 89.7% 1.8% 97.6% 0.7 0.9AS !7 at 5 min 8.3% 83.2% 0.6% 97.5% 0.5 0.9 0 89.7% 0 98.8% 0 0.8UApH !7.10 7.1% 83.1% 0.9% 96.9% 0.4 0.8 5.9% 89.6% 1.8% 96.8% 0.6 0.9UApH !7.00 50% 83.5% 0.3% 99.8% 3.0 1.6 0 89.7% 0 99.6% 0 0.8

Sens, Sensitivity; Spec, specificity; PPV, positive predictive value; NPV, negative predictive value .

pocket. Despite the increased rate of intervention, 2major outcomes of concern, cesarean delivery for non-reassuring FHR and neonatal acidosis, were similar inthe 2 groups.

Second, because of a false-positive test, iatrogenicprematurity does occur when modified biophysical isused for antepartum surveillance. While we noted itsrate to be 2%, Miller et al17 reported that it was 1.5%.Though this complication was similar for the 2 groups,it may be due to the small sample size of this study. Wedid note a significantly higher rate of RDS among thosewho had assessment of amniotic fluid using the indexrather than the single deepest pocket. The pretermdeliveries in 5 of the 6 cases of RDS were secondaryto medical (hypertension) or obstetric (spontaneouspreterm labor) complications and use of AFI spuriouslyinfluenced the rate of RDS. Only one case of pretermdelivery and RDS was secondary to the finding of AFI!5.0 cm. Thus, iatrogenic prematurity with associatedcomplications, we think, occurs in 2% (1/47; 95% CI0.05e11) of the cohorts that are managed with the use of

AFI. Randomized clinical trials with a larger sample sizeare needed to determine a more precise risk of iatrogenicRDS with use of AFI in the modified BPP.

The third finding of this trial is that both methods ofdetermining amniotic fluid are poor diagnostic tests inidentifying peripartum complications (Table IV). Pres-ently, there is a debate about the diagnostic ability ofAFI to predict adverse outcomes. While Casey et al3

noted that with the use of AFI, antepartum detection ofoligohydramnios is associated with increased perinatalmorbidity and mortality, Magann et al6 considered AFIto be a poor diagnostic test. The limitation of thesereports3,6 is that they were not randomized clinical trials,and the investigators did not report the likelihood ratio,a preferred way to evaluate a diagnostic test.

The findings of this study are consistent with theprevious report by Alfirevic et al,11 who randomizeduncomplicated, post-term patients (gestational age of 290days or more) to be monitored with computerizedcardiotocography with AFI or maximum deepest pocket.These investigators considered the amniotic fluid to be

666 Chauhan et al

abnormal if the AFI was less than 7.3 cm or if themaximumdeepest pocketwas!1.8 cm, both ofwhich arebelow the third percentile for 42 weeks. Despite thedifferences in the definition of inadequate amniotic fluidbetween our study and this published report,11Alfirevic etal’s study also noted that significantly more post-termpatients were diagnosed with oligohydramnios, and weresubsequently induced if the AFI was used for antepartumsurveillance. Both our randomized study and that ofAlfirevic et al11 noted that the rate of cesarean delivery fornonreassuring FHR tracing and neonatal acidosis weresimilar, regardless of which technique was used toestimate the amniotic fluid volume.

Amniotic fluid volume assessment is important in thesurveillance of high-risk pregnancies. A low amnioticfluid volume is thought to represent inadequate utero-placental perfusion with the shunting of blood to thefetal heart, adrenals, and brain with resultant poor renalperfusion and a reduced fetal urinary output. Before theinvestigations by Phelan et al4 suggesting that the AFIbe used to evaluate amniotic fluid volume, the singledeepest pocket was routinely used, and the definition ofoligohydramnios was the absence of a 1!1 or 2!1 cmpocket.5 Surprisingly, without the benefit of a random-ized clinical trial, the AFI was substituted for the singledeepest pocket technique to estimate amniotic fluidvolume. A possible reason for this substitution werethe reports by Rutherford et al19 and Sarno et al,20

which noted that AFI %5.0 cm was significantlyassociated with an increased rate of cesarean deliveryfor nonreassuring FHR tracing and low Apgar scores.What was overlooked in this substitution was thesubjective nature of these 2 end points.

The incidence of neonatal acidosis, an objectiveassessment of fetal well-being, with AFI % vs O5.0cm was not even addressed in the early reports.19,20

Subsequently, a meta-analysis of 42 reports over 10years found only one study which correlated the rate ofumbilical arterial pH !7.00 with AFI, and noted thatneonatal acidosis occurs with similar frequency amonghigh-risk patients with AFI %5.0 cm as those with O5.0cm.10 More recent works by Magann et al6 and Caseyet al3 have also not linked pH!7.00 with AFIO5.0 cm.If there is no association between pathologic acidosisand AFI, then continued use of this technique to assessamniotic fluid is unnecessary, especially because ran-domized clinical trials indicate an increase rate ofintervention without improved outcome.

The major shortcoming of this randomized trial isthat the sample size was inadequate to evaluate mean-ingful, unambiguous outcomes like cerebral palsy orneonatal death. But considering the infrequent occur-rence of these events, a randomized clinical trial todecrease their rate is a formidable undertaking. Assum-ing that umbilical arterial pH !7.00 occurs in 0.4%,then 8700 patients in each group are necessary to detect

a 20% reduction in prevalence between the study arms(two-tailed alpha of 0.05 and power of 80%). It isnoteworthy that Manning et al21 did report that with theuse of the complete BPP they were able to significantlyreduce the rate of cerebral palsy among high-risk pa-tients. Specifically, they noted that the incidence of cere-bral palsy among the general population (3.7 per 1000live births) was significantly higher than the high-riskparturients who had BPP (1.3 per 1000 live births; P !.0001). Admittedly, several criteria have been used to en-sure adequate fluid during the BPPs,5 but none of themincluded use of AFI. Thus, if modified BPP is to besubstituted for the 5 variables survey, then we shoulduse one of the definitions used by Manning et al.21

In conclusion, use of single deepest pocket withmodified BPP would decrease the rate of induction forsuspected oligohydramnios. Unless randomized clinicaltrials show benefit of summing the measurements of 4quadrants over dimensions of the deepest pocket, use ofAFI during modified BPP should be avoided.

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3. Casey BM, McIntire DD, Bloom SL, Lucas MJ, Santos R,

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Lange IR. Ultrasound evaluation of amniotic fluid volume. I.

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Chauhan et al 667

Discussion

DR WILLIAM A. NEWTON, Tampa, Fla. Oligohydramnioshas been demonstrated by a number of studies as anominous prognostic sign of fetal well-being, especially inthe high-risk and postdate pregnancy.1-3 There havebeen links between decreased amniotic fluid volume tostillbirth, fetal anomaly, abnormal fetal heart ratetracings in labor, increase in cesarean section for fetaldistress, and possibly fetal acidosis.4 The concept of 4-quadrant fluid measurement for amniotic fluid volume(AFV) was introduced in the mid 1980s. Since that timeamniotic fluid index (AFI) has been widely accepted asan accurate means of defining oligohydramnios and itsrelationship to fetal compromise.2 However, in the pastseveral years AFI has increasingly been questioned asthe appropriate standard measurement to define oligo-hydramnios.5

Because many authors have noted that amniotic fluidvolume alone may be a poor predictor of fetal well-being6 there has been the evolution of amniotic fluidvolume incorporated into other diagnostic tests such asthe biophysical profile and the modified biophysicalprofile. These fetal assessment tests greatly enhance safemanagement of the high-risk pregnancy but may alsoresult in unwarranted intervention and morbidity.

Dr Chauhan’s study compares AFI versus measure-ment of a 2!1-cm single deepest pocket (SDP) in-corporated into the modified biophysical profile asa predictor of fetal compromise. His results imply thatAFI is not only less specific than SDP but more likely toresult in a higher potential for unnecessary interventionthrough increased induction of labor for oligohydram-nios. Using AFI with modified biophysical profileresulted in a 2% iatrogenic prematurity rate in thisstudy. These findings seem contradictory to the 1987study by Rutherford et al,7 which looked at 330 high-risk pregnancies comparing 4-quadrant AFV assessmentand SDP. In that study AFI was found to have a highrelationship to low Apgar score and cesarean section forfetal distress. Following Rutherford’s study the AFI wasused as measurement of amniotic fluid volume for themodified biophysical profile. Coinciding with the accep-tance of AFI as routine part of obstetric ultrasound,induction of labor for oligohydramnios increased from26% in 1991 to 75% in 1996.

In Dr Chauhan’s study, intrapartum oligohydram-nios was diagnosed in 17% by AFI and only 10% bySDP. However, there was no significant difference inpredictability of cesarean section for fetal distress, lowApgar score, or umbilical pH !7.1. Of note, cliniciansmanaging labor were aware of whether oligohydramnioswas determined by AFI or SDP. There was also theimplication that AFI measurement was associated withincreased potential morbidity, as noted by 13 more AFIpatients undergoing amnioinfusion for presumed fetaldistress. Admission to the NICU for transient tachypneaof the newborn and respiratory distress syndromeoccurred in 12 more patients with AFI vs SDP, implyingthat in a larger sample size, AFI may be statisticallyassociated with a higher iatrogenic morbidity than SDP.AFI as well as SDP are ‘‘poor diagnostic tests’’ foridentifying peripartum complications. If used in themodified biophysical profile, the SDP should decreasethe rate of induction of labor for suspected oligohy-dramnios.

This study is impressive, but a much larger samplesize is needed to look at the best method of determiningoligohydramnios. For that matter, defining exactly whatoligohydramnios is quantitatively and in what circum-stance it reflects a poor prognostic sign is needed. Themodified biophysical profile with assessment of AFV isan easy and convenient test for the evaluation of thehigh-risk patient. A reliable consensus standard ofmeasurement is essential for a uniform diagnostic test.

Dr Chauhan et al are congratulated on this interest-ing prospective clinical study. My questions for DrChauhan are: (1) in your study, the managing clinicianswere aware of the method of determining oligohydram-nios. Don’t you feel that this may have resulted inclinician bias in the management of individual cases? (2)What role, if any, do you feel that evolving technology

668 Chauhan et al

in ultrasonography has played in your study vs thoselooking at AFI 15 years ago?

References

1. Hoskins IA, Frieder FJ, Young BK. Variable decelerations in

reactive nonstress tests with decreased AFI predicts fetal compro-

mise. Am J Obstet Gynecol 1991;165:1094-8.

2. Chauhan SP, Sanderson M, Hendrix NW, Magann EF, Devoe LD.

Perinatal outcome and amniotic fluid index in the antepartum and

intrapartum periods: a meta-analysis. Am J Obstet Gynecol

1999;181:1473-8.

3. Phelan JP, Platt LD, Yeh SY, Broussard P, Paul RH. The role of

ultrasound assessment of amniotic fluid in the management of the

posdate pregnancy. Am J Obstet Gynecol 1985;151:304-8.

4. Bastide A, Manning F, Harman C, Lange I, Morrison I. Ultra-

sound evaluation of amniotic fluid: outcome of pregnancies with

severe oligohydramnios. Am J Obstet Gynecol 1986;154:895-900.

5. Rainford M, Adair R, Scialli AR, Ghidini A, Spong CY. Amniotic

fluid index in the uncomplicated term preganancy. J Reprod Med

2001;46:589-92.

6. Magann EF, Kinsella MJ, Chauhan SP, McNamara MF,

Gehring BW, Morrison JC. Does an amniotic fluid index of %5

cm necessitate delivery in high risk pregnancies? A case-controlled

study. Am J Obstet Gynecol 1999;180:1354-9.

7. Rutherford SE, Phelan JP, Smith CV, Jacobs N. The four-quadrant

assessment of amniotic fluid volume: an adjunct to antepartum fetal

heart rate testing. Obstet Gynecol 1987;70:353-6.

8. 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 200;182:909e12.

DR TOLEDO (Closing). I truly appreciate the thoughtfulcomments and insightful questions by Dr Newton. Theclinicians were aware of the techniques used to de-termine if the patient had oligohydramnios, and thoughthis knowledge may have resulted in bias, it could not beavoided. Additionally, in actual practice, the clinicianwill know whether amniotic fluid index or single deepestpocked was used to assess fluid. Thus, the design of thestudy does mirror actual practice.

The question about evolving technology and itsimpact on assessing amniotic fluid is excellent. Ifanything, with increasing resolution, oligohydramniosshould be diagnosed less frequently than before, butwith increasing availability of ultrasound machines onlabor and delivery, we may be labeling too manypatients as having oligohydramnios if we continue touse AFI.