title: Yolk sac volume assessed by three-dimensional ultrasonography using the VOCAL method.
abstract: OBJECTIVE
  Establish normative data for yolk sac volume (YSV) at 7-10 weeks of gestation assessed by transvaginal three-dimensional ultrasonography (3D-US) using the VOCAL method and analyze its correlation with gestational age (GA) and crown-rump length (CRL).
  
  
  METHODS
  A cross-sectional study involving 62 normal pregnancies was performed to assess YSV from 7 to 10 weeks of gestational age. An endocavitary volumetric transducer (3D5-8EK) was used for all measurements. The VOCAL (Virtual Organ Computer-aided AnaLysis) method with a 30 degrees rotation angle was used for volumetric calculations. Regression models were constructed to analyze the correlation between YSV and GA or CRL The mean, standard deviation, median, minimum and maximum values were calculated for each gestational age.
  
  
  RESULTS
  There was a poor correlation between YSV and GA or CRL. The quadratic regression was the model that best expressed the correlation between these variables: R2=0.188 for GA and R2=0.203 for CRL. The mean YSV went from 0.063 cm(3) (95% CI: 0.047; 0.080) at 7 weeks to 0.164 cm3 (95% CI 0.095; 0.232) at 10 weeks.
  
  
  CONCLUSIONS
  Reference limits were generated for first trimester YSV using 3D-US. There was a poor correlation between YSV and GA or CRL.
authors.affiliation: Department of Obstetrics, São Paulo Federal University (UNIFESP - EPM), São Paulo, SP, Brazil.
authors.forename: Líliam Cristine
authors.initials: LC
authors.lastname: Rôlo
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; D003430:Cross-Sectional Studies; D018568:Crown-Rump Length; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012044:Regression Analysis; D016216:Ultrasonography, Prenatal / Q000379:methods*; D015017:Yolk Sac / Q000000981:diagnostic imaging*