title: Normal values for amniotic fluid index during uncomplicated twin pregnancy.
abstract: OBJECTIVE
  To establish the gestational age trends of amniotic fluid index (AFI) in uncomplicated twin pregnancies.
  
  
  METHODS
  Amniotic fluid index was measured in uncomplicated twin pregnancies seen between 1985 and 1993 and meeting the following criteria: 1) no maternal medical or obstetric complications, 2) normal growth of both twins by serial ultrasound, and 3) normal amniotic fluid volume by ultrasound. Amniotic fluid index was measured by adding the deepest vertical pockets in four quadrants, defined by the umbilicus and linea nigra. The relation between gestational age and AFI was evaluated using linear regression analysis.
  
  
  RESULTS
  Two hundred eighty-two sets of twins were considered uncomplicated; 1101 AFI measurements were performed on these pregnancies between 25.5 and 40.5 weeks' gestation. Percentile values for AFI were determined according to gestational age. The regression equation relating the median AFI to gestational age was: AFI = 19.4 - 0.12 x gestational age (P = .03). The R2 value was 0.04.
  
  
  CONCLUSIONS
  Gestational age trends in normative AFI measurements for twin pregnancies have been established. Their use will facilitate a more reproducible, quantitative diagnosis of oligohydramnios in twins, compared with subjective, qualitative approaches to amniotic fluid volume assessment.
authors.affiliation: Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, USA.
authors.forename: T F
authors.initials: TF
authors.lastname: Porter
authors.forename: G A
authors.initials: GA
authors.lastname: Dildy
authors.forename: J R
authors.initials: JR
authors.lastname: Blanchard
authors.forename: N K
authors.initials: NK
authors.lastname: Kochenour
authors.forename: S L
authors.initials: SL
authors.lastname: Clark
mesh_terms: D000328:Adult; D000653:Amniotic Fluid / Q000000981:diagnostic imaging*; D005260:Female; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D016104:Oligohydramnios / Q000000981:diagnostic imaging; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D014427:Twins; D016216:Ultrasonography, Prenatal