title: Curve of amniotic fluid index measurements in low-risk pregnancy.
abstract: OBJECTIVE
  To establish a curve of amniotic fluid index [AFI] measurements from the 20th to the 42nd week of pregnancy.
  
  
  METHODS
  A prospective and descriptive study was performed, in which an independent sample of 2,868 low-risk pregnant women were studied using routine ultrasound, including fetal biometry and measurement of AFI. Data were analysed using multiple linear regression, and constructing a curve using 2.5th, 10th, 50th, 90th and 97.5th percentiles of the AFI measurements, according to gestational age, and after submitting values to smoothing process using quadratic polynomial adjustment.
  
  
  RESULTS
  There was a significant variation in AFI measurements at the different gestational ages. The 50th percentile remained practically constant at approximately 150 mm between the 20th and 33rd week, after which there was a decline in volume, which became evident after the 38th week. At the 40th week, the 10th percentile was around 62 mm and the 2.5th percentile around 33 mm.
  
  
  CONCLUSIONS
  The curve of percentiles of AFI measurements in low-risk pregnant women showed significant decrease with gestational age, especially after the 33rd week. These data should be validated for a diagnosis of increased or decreased volumes of amniotic fluid at specific gestational ages.
authors.affiliation: Department of Obstetrics and Gynecology, University of Campinas (UNICAMP), Campinas, Brazil.
authors.forename: Maria Regina
authors.initials: MR
authors.lastname: Machado
authors.forename: Jose Guilherme
authors.initials: JG
authors.lastname: Cecatti
authors.forename: Fabiana
authors.initials: F
authors.lastname: Krupa
authors.forename: Anibal
authors.initials: A
authors.lastname: Faundes
mesh_terms: D000293:Adolescent; D000328:Adult; D000653:Amniotic Fluid / Q000000981:diagnostic imaging / Q000502:physiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D008875:Middle Aged; D011247:Pregnancy / Q000502:physiology*; D011262:Pregnancy Trimester, Second / Q000502:physiology; D011263:Pregnancy Trimester, Third / Q000502:physiology; D011446:Prospective Studies; D012016:Reference Values; D016216:Ultrasonography, Prenatal