title: The amniotic fluid index, single deepest pocket, and two-diameter pocket in normal human pregnancy.
abstract: OBJECTIVE
  This study was undertaken to determine normative values for amniotic fluid index, single deepest pocket, and 2-diameter pocket across gestation.
  
  
  METHODS
  Fifty patients with normal pregnancies at each gestational age between 14 and 41 weeks' gestation were recruited prospectively and scanned once. Data were transformed into logarithmic (base 10) values for analysis. Polynomial regression equations were used to predict the normal values for amniotic fluid index, single deepest pocket, and 2-diameter pocket across gestational age and to predict the weekly percentage changes.
  
  
  RESULTS
  The mean amniotic fluid index, single deepest pocket, and 2-diameter pocket values were significantly lower among patients at <37 weeks' gestation (n = 1150) than among those at > or =37 weeks' gestation (n = 250; P <.001 for all comparisons). The calculated prevalences of oligohydramnios (amniotic fluid index < or =5 cm, single deepest pocket <2 cm, or 2-diameter pocket <15 cm(2)) were significantly different (P <.0001) for the three techniques (8%, 1%, and 30%, respectively). Hydramnios (amniotic fluid index >24 cm, single deepest pocket >8 cm, or 2-diameter pocket >50 cm(2)) was also diagnosed with significantly different (P <.0001) frequencies (0%, 0.7%, and 3%, respectively).
  
  
  CONCLUSIONS
  This is the largest prospective study to date to provide normative data for each of three ultrasonographic techniques used to assess amniotic fluid volume. The single deepest pocket appears to be the preferable method, because its use is least likely to lead to the false-positive diagnosis of either oligohydramnios or hydramnios.
authors.affiliation: Department of Obstetrics and Gynecology, University of Mississippi Medical Center, Jackson, USA.
authors.forename: E F
authors.initials: EF
authors.lastname: Magann
authors.forename: M
authors.initials: M
authors.lastname: Sanderson
authors.forename: J N
authors.initials: JN
authors.lastname: Martin
authors.forename: S
authors.initials: S
authors.lastname: Chauhan
mesh_terms: D000328:Adult; D000653:Amniotic Fluid / Q000000981:diagnostic imaging / Q000378:metabolism*; D005260:Female; D005865:Gestational Age; D006801:Humans; D016104:Oligohydramnios / Q000000981:diagnostic imaging / Q000453:epidemiology; D006831:Polyhydramnios / Q000000981:diagnostic imaging / Q000453:epidemiology; D011247:Pregnancy / Q000378:metabolism*; D011296:Prenatal Diagnosis; D015995:Prevalence; D011446:Prospective Studies; D012016:Reference Values; D014463:Ultrasonography / Q000379:methods