title: Nomogram of amniotic fluid volume at 7 to 10+6 weeks of pregnancy by three-dimensional ultrasonography using the rotational method (VOCAL).
abstract: OBJECTIVE
  To establish normative data for amniotic fluid volume (AFV) between 7 and 10+6 weeks gestation using three-dimensional ultrasonography (3DUS).
  
  
  METHODS
  A cross-sectional study involving 74 normal pregnancies was performed to assess AFV. All measurements were performed using an endocavitary volumetric transducer. The VOCAL (virtual organ computer-aided analysis) method was used for volumetric calculations, with a 30 degrees rotation angle. The AFV was obtained subtracting the embryonic volume from the amniotic sac volume. To analyze the correlation between AFV and gestational age, regression models were constructed and adjustments were made using the determination coefficient (R2). The following AFV values were obtained for each week: mean, median, standard deviation, minimum and maximum. The method proposed by Royston and Wright was used to calculate the reference intervals according to crown-rump length (CRL).
  
  
  RESULTS
  Mean AFV increased from 3.97 cm3 (range 1.17-10.97 cm3) at 7 to 7+6 weeks to 23.33 cm3 (ranging from 11.93 to 32.41 cm3) at 10 to 10+6 weeks of pregnancy. There was a significant correlation between AFV and gestational age (R2=0.635) and between AFV and CRL (R2=0.756). Mean AFV increased from 7.81 cm3 (ranging from 0.18 to 15.43 cm3) to 50.28 cm3 (range 16.49-84.07 cm3) for CRL between 12 and 40 mm.
  
  
  CONCLUSIONS
  Reference limits for AFV using 3DUS were generated for pregnancies between 7 and 10+6 weeks according to CRL.
authors.affiliation: Department of Obstetrics, Sao Paulo Federal University (UNIFESP), São Paulo, SP, Brazil.
authors.forename: Liliam Cristine
authors.initials: LC
authors.lastname: Rolo
authors.forename: Luciano Marcondes Machado
authors.initials: LM
authors.lastname: Nardozza
authors.forename: Edward
authors.initials: E
authors.lastname: Araujo Júnior
authors.forename: Paulo Martin
authors.initials: PM
authors.lastname: Nowak
authors.forename: Antonio Fernandes
authors.initials: AF
authors.lastname: Moron
mesh_terms: D000328:Adult; D000653:Amniotic Fluid / Q000000981:diagnostic imaging / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D049451:Nomograms; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D012016:Reference Values; D016216:Ultrasonography, Prenatal / Q000379:methods*; D055815:Young Adult