title: Amnioreduction: how much to drain?
abstract: OBJECTIVE
  To assess the relationship between the volume of amniotic fluid removed and the change in amniotic fluid index (AFI) and calculate an equation describing this association.
  
  
  METHODS
  A retrospective analysis of 19 amnioreduction procedures performed in our unit. Multiple regression analysis was used to assess the effect of gestational age and pre-procedure AFI on the change in AFI (DeltaAFI) after adjusting for the volume removed.
  
  
  RESULTS
  As expected, a significant linear relationship was found between the change in AFI and the volume removed (r = 0.82, n = 19, p < 0.0001). DeltaAFI was not dependent on the gestational age or the pre-procedure AFI. The equation describing the association between the volume removed and DeltaAFI was: volume = (DeltaAFI - 2. 26)/0.008, which is close to 1 cm DeltaAFI for every 100 ml removed.
  
  
  CONCLUSIONS
  Using the described equation, it is possible to predict the required volume to be removed in order to achieve a particular DeltaAFI, which may reduce the need to interrupt the procedure to measure the AFI. However, the limitation of AFI as a semiquantitative assessment of the liquor volume, together with its inter- and intra-observer variations mean this equation should be used only as a guide.
authors.affiliation: Fetal Medicine Research Unit, St Michael's Hospital, Bristol, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Abdel-Fattah
authors.forename: S G
authors.initials: SG
authors.lastname: Carroll
authors.forename: P M
authors.initials: PM
authors.lastname: Kyle
authors.forename: P W
authors.initials: PW
authors.lastname: Soothill
mesh_terms: D000653:Amniotic Fluid; D004322:Drainage; D005260:Female; D006801:Humans; D008962:Models, Theoretical; D006831:Polyhydramnios / Q000000981:diagnostic imaging / Q000601:surgery*; D011247:Pregnancy; D011272:Pregnancy, Multiple; D012044:Regression Analysis; D012189:Retrospective Studies; D014427:Twins; D014463:Ultrasonography