title: Association and prediction of amniotic fluid measurements for adverse pregnancy outcome: systematic review and meta-analysis.
abstract: BACKGROUND
  Measurements of amniotic fluid volume are used for pregnancy surveillance despite a lack of evidence for their predictive ability.
  
  
  OBJECTIVE
  To evaluate the association and predictive value of ultrasound measurements of amniotic fluid volume for adverse pregnancy outcome.
  
  
  METHODS
  Electronic databases (inception to October 2011), reference lists, hand searching of journals, contact with experts.
  
  
  METHODS
  Studies comparing measurements of amniotic fluid volume with adverse outcome, excluding pre-labour ruptured membranes or congenital/structural anomalies.
  
  
  METHODS
  Data on study characteristics, design, quality. Random effects meta-analysis to estimate summary odds ratios (prognostic association) and summary sensitivity, specificity and likelihood ratios (predictive ability).
  
  
  RESULTS
  Forty-three studies (244,493 fetuses) were included demonstrating a strong association between oligohydramnios (varying definitions) and birthweight <10th centile (summary odds ratio [OR] 6.31, 95% confidence interval [95% CI] 4.15-9.58; high-risk population [author definition] n = 6 studies, 28,510 fetuses), and mortality (neonatal death any population summary OR 8.72, 95% CI 2.43-31.26; n = 6 studies, 55,735 fetuses; and perinatal mortality high-risk population summary OR 11.54, 95% CI 4.05-32.9; n = 2 studies, 27;891 fetuses). There was a strong association between polyhydramnios (maximum pool depth >8 cm or amniotic fluid index ≥25 cm) and birthweight >90th centile (OR 11.41, 95% CI 7.09-18.36; n = 1 study, 3960 fetuses). Despite strong associations, predictive accuracy for perinatal outcome was poor.
  
  
  CONCLUSIONS
  Current evidence suggests that oligohydramnios is strongly associated with being small for gestational age and mortality, and polyhydramnios with birthweight >90th centile. Despite strong associations with poor outcome, they do not accurately predict outcome risk for individuals.
authors.affiliation: Birmingham Centre for Women's & Children's Health & School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK; Fetal Medicine Centre, Birmingham Women's Hospital NHS Foundation Trust, Birmingham, UK.
authors.forename: R K
authors.initials: RK
authors.lastname: Morris
authors.forename: C H
authors.initials: CH
authors.lastname: Meller
authors.forename: J
authors.initials: J
authors.lastname: Tamblyn
authors.forename: G M
authors.initials: GM
authors.lastname: Malin
authors.forename: R D
authors.initials: RD
authors.lastname: Riley
authors.forename: M D
authors.initials: MD
authors.lastname: Kilby
authors.forename: S C
authors.initials: SC
authors.lastname: Robson
authors.forename: K S
authors.initials: KS
authors.lastname: Khan
mesh_terms: D000653:Amniotic Fluid / Q000000981:diagnostic imaging*; D001724:Birth Weight; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016017:Odds Ratio; D016104:Oligohydramnios / Q000000981:diagnostic imaging* / Q000401:mortality; D006831:Polyhydramnios / Q000000981:diagnostic imaging* / Q000401:mortality; D011237:Predictive Value of Tests; D011247:Pregnancy; D011256:Pregnancy Outcome; D011379:Prognosis; D015203:Reproducibility of Results; D016216:Ultrasonography, Prenatal / Q000379:methods
keywords: Amniotic fluid; oligohydramnios; predictive accuracy; prognosis; small for gestational age