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A Systematic Review of Amniotic Fluid Assessments in Twin Pregnancies Danielle L. Ippolito, PhD, Jennifer E. Bergstrom, MD, Monica A. Lutgendorf, MD, Shannon K. Flood-Nichols, DO, Everett F. Magann, MD

Received October 10, 2013, from the Department of Clinical Investigation (D.L.I.) and Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology (M.A.L., S.K.F.-N.), Madigan Army Medical Center, Tacoma, Washington USA; Department of Obstetrics and Gynecology, Naval Medical Center, Portsmouth, Virginia USA (J.E.B.); and Department of Obstetrics and Gynecology, University of Arkansas for the Medical Sciences, Little Rock, Arkansas USA (E.F.M.). Revision requested October 28, 2013. Revised manuscript accepted for publication November 25, 2013. We thank Cindy Kirker of Madigan Army Medical Center’s Medical Library for article procurement and library support on this project and Donna Eastham, BA, of the University of Arkansas for Medical Sciences for help with manuscript preparation and submission. The views expressed herein are those of the authors and do not reflect the official policy of the Department of the Army, the Department of the Navy, or the Department of Defense. Address correspondence to Everett F. Magann, MD, Department of Obstetrics and Gynecology, University of Arkansas for the Medical Sciences, 4301 W Markham St, Slot 518, Little Rock, AR 72205-7199 USA. E-mail: [email protected] Abbreviations

AFI, amniotic fluid index; AFV, amniotic fluid volume; GA, gestational age; NICU, neonatal intensive care unit; SDP, single deepest pocket; 2DP, 2-diameter pocket; TTTS, twin-twin transfusion syndrome doi:10.7863/ultra.33.8.1353

The objectives of this systematic review were to examine the reproducibility of sonographic estimates of amniotic fluid volume (AFV) in twin pregnancies, compare the association of sonographic estimates of AFV with dye-determined AFV, and correlate AFV with antepartum, intrapartum, and perinatal outcomes in twin pregnancies. Studies were included if they were adequately powered and investigated antepartum, intrapartum, and/or perinatal adverse outcome parameters in twin gestations. Studies with comparable populations and exclusion criteria were merged into forest plots. Data comparing the accuracy of AFV assessment, correlation of AFV with gestational age, and adverse outcomes were tabulated. Five of the 6 studies investigating AFV by the amniotic fluid index as a function of gestational age reported data fitting a quadratic equation, with fluid volumes peaking at mid gestation and then declining. This trend was less pronounced when AFV was assessed by the single deepest pocket (2 of 4 studies reporting a quadratic fit). Polyhydramnios was associated with prematurity in 2 of 4 studies (1 amniotic fluid index and 1 single deepest pocket), and oligohydramnios was associated with prematurity in 1 single deepest pocket study. Stillbirth was the only intrapartum outcome reported in more than 1 study. Perinatal outcomes associated with polyhydramnios included neonatal death (P < .05 in 1 of 2 studies), low Apgar scores (1 of 2 studies), neonatal intensive care unit admission (1 of 2 studies), and low birth weight (2 of 3 studies). Key Words—amniotic fluid volume; obstetric ultrasound; sonography; twin pregnancies


mniotic fluid volume (AFV) is normally estimated by sonographic assessment as part of routine obstetric care. In singleton gestations, deviations from normal AFV (eg, oligohydramnios and polyhydramnios) have been associated with complications, including fetal anomalies, postmaturity syndrome, fetal growth restriction, congenital abnormalities, and diabetes.1,2 Singleton pregnancies complicated by oligohydramnios may present with comorbid fetal renal anomalies, central nervous system anomalies, or infections. Pregnancies with severe oligohydramnios are at high risk for fetal or neonatal death.3 In twins, substantial fluid volume discordance between sacs can be a clinical indicator of twintwin transfusion syndrome (TTTS).4–6 Twin pregnancies are at a significantly higher risk for perinatal morbidity and mortality.7,8 However, few studies have directly investigated whether an abnormal AFV has predictive value in twin gestations outside TTTS.

©2014 by the American Institute of Ultrasound in Medicine | J Ultrasound Med 2014; 33:1353–1364 | 0278-4297 | www.aium.org

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Subjective scales have been developed and used to diagnose changes in fluid volume over gestational time.9,10 The most accurate methods for quantitatively assessing AFV are measuring the fluid volume at the time of delivery and calculating the AFV by the dye dilution technique of Charles and Jacoby.11 Concordance has been demonstrated between dye-determined AFV and direct measurement of AFV at the time of cesarean delivery (r = 0.99).12 However, AFV measurement at delivery cannot be used to serially monitor antepartum fluid volumes, and the dye dilution technique is time-consuming and invasive, and it requires specialized laboratory support after hysterotomy. These limitations have led to use of sonography to estimate the AFV. Sonographic measurements of AFV include amniotic fluid index (AFI), single deepest pocket (SDP), and 2-diameter pocket (2DP) techniques.13 The AFI was first described in 1987 by Phelan et al,14 and the SDP was introduced in 1980.15 In singleton pregnancies, these methods are used routinely as part of biophysical tests for monitoring fetal well-being in the second and third trimesters of pregnancy.16 The use of sonographic measurements in twin gestations is complicated by the dividing membrane in diamniotic twins. This membrane can compromise the accuracy of sonographic volume assessment in twin pregnancies.7 The accuracy of sonographic methods in making longitudinal assessments of AFV over time is also unclear in twin pregnancies. Furthermore, it is unclear whether AFV abnormalities are also associated with adverse outcomes in twins, as has been observed in singleton pregnancies. The objective of this study was to conduct a systematic review of the literature describing the sonographic estimates of AFV, their correlation with dye-determined AFV, and the association of twin AFV with antepartum, intrapartum, and perinatal outcomes.

excluded (>10 patients enrolled in the study). All reports were written in English. Any relevant data summarized in review articles were evaluated by accessing the pertinent manuscripts. End points for data assessment included comparison of sonographic methods (AFI versus SDP versus subjective assessment) in twins compared to singleton pregnancies, changes in fluid volume with advancing gestational age (GA) in twin pregnancies, and differences in AFV throughout pregnancy in monochorionic diamniotic and dichorionic diamniotic twins. Amniotic fluid volumes were segregated according to published criteria for oligohydramnios, polyhydramnios, or normal fluid volumes. The review process is summarized in Figure 1.

Results Study Selection Figure 1 illustrates the final schematic for selecting studies for inclusion. A total of 94 studies were retrieved from PubMed as described in “Materials and Methods.” Eleven duplicate records were identified on the Web of Science. Duplicate records were removed. Two of the authors (J.E.B. and D.L.I.) reviewed all of the abstracts for the resulting 94 studies (Figure 1). Full articles were reviewed for all abstracts selected for inclusion by 1 or both of the reviewers(n = 43 articles) by 2 authors (J.E.B. and S.K.F.-N.). Of the 43 reports, 24 were excluded because of improper controls, TTTS, too few cases, review articles, and case studies. If there was a discrepancy among authors on an article, a third reviewer (M.A.L.) also reviewed the article Figure 1. Schematic of the abstract and article screening selection process.

Materials and Methods Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2009 guidelines were used to assess available articles for inclusion eligibility and to construct this systematic review.17 Both PubMed and the Web of Science were searched between January 1, 1980, and December 31, 2012, for search terms including “amniotic fluid,” “volume,” “cc,” “mL,” “twin,” “twins,” and “multiple birth.” During the review process, an additional study was added from June 2013.18 Study eligibility characteristics were twin pregnancies evaluated for AFV by either sonography or the dye exclusion method and AFV assessment throughout pregnancy. Case reports and case series were


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and determined whether it was to be included. The reports proceeding to the final analysis and inclusion in the systematic review were subdivided into categories: measurement, outcomes, both, and exclude. Two more reviewers (S.K.F.-N. and E.F.M.) evaluated the articles designated for the final analysis. The final analysis included reports powered to investigate the following end points: measurements only (n = 16), outcomes only (n = 1), and outcomes and measurements (n = 3). Table 1 lists the parameters of the studies included in the final analysis and whether they were used to assess measurements, outcomes, or both.1–3,9,18–32 Table 2 lists the studies included for abnormal AFV and adverse outcomes in twins.3,31–33

Measurement Methods in Normal Twins The studies used to assess methods of amniotic fluid measurement in normal twins are listed in Table 1. Studies were grouped according to the type of comparison tested in twins: (1) association between the dye dilution and sonographic estimate; (2) association between AFV and GA; (3) incidence of oligohydramnios or polyhydramnios; (4) intra- and inter-amniotic fluid measurements in each sac; (5) discordance; and (6) comparison between singleton and twin pregnancies.

Table 1. Longitudinal Studies on AFV


Study Period

Type of Twin

Fluid discordance over gestational time Schneider, 1985 1979–1983 MC Chescheir, 1988 1982–1987 DA Lange, 1989 1983 DA Patten, 1989 1979–1987 MCDA Rådestad, 1990 1980–1987 MCDA

Study Design

GA Range, Pregnancies, wk n Method

Case series 23–30 Case series 2-delivery Intervention 22–37 Prospective 17–28 Retrospective 21–35

Absolute amniotic sac volume over gestational time Magann, 1995 Not stated DA Prospective (OBGYN ) Magann, 1995 Not stated DA Prospective (JSGI )

DA DA Not stated MCDA DA

Subjective Subjective SDP Subjective Not stated

NA NA ≤2 cm NA NA

NA NA 2.1–8.0 cm NA NA

NA NA >10 cm NA >3-cm change in 1 wk



Dye dilution

2100 mL



2DP SDP AFI Dye dilution SDP AFI, SDP, 2DP AFI AFI SDP, dye dilution Dye dilution

8 cm dye dilution AFI 0–5 cm AFI 5–20 cm AFI >20 cm 2DP 0–15 cm2 2DP 15–50 cm2 2DP >50 cm2 SDP 7.5 cm

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A systematic review of amniotic fluid assessments in twin pregnancies.

The objectives of this systematic review were to examine the reproducibility of sonographic estimates of amniotic fluid volume (AFV) in twin pregnanci...
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