title: Longitudinal distance standards of fetal growth. Intrauterine and Infant Longitudinal Growth Study: IILGS.
abstract: BACKGROUND
  Most ultrasonographic fetal growth norms are derived from cross-sectional data or from longitudinal data treated as coming from cross-sectional studies, although only longitudinal models may detect particular aspects of fetal growth shape, such as peak of growth velocity.
  
  
  METHODS
  The sample included 238 singleton normal pregnancies. All the fetal traits under study (biparietal diameter, occipito-frontal diameter, head circumference, femur diaphysis length and abdomen circumference) were measured according to the classical ultrasound techniques by highly trained operators. Individual growth profiles (made up of 5 to 9 measures) were taken at regular intervals between the 12th and the 40th week. Growth norms were traced by means of a two-stage linear model: (I) a 3-constant fetal growth function was fitted to each individual growth profile, (II) growth centiles were based upon the weighted mean and covariance matrix of the individual growth constants.
  
  
  RESULTS
  Fetal growth curves show a sigmoid shape with a maximum slope (i.e. a peak growth velocity) which occurs earlier for head diameters (about 18 weeks), later for femur diaphysis length (20 weeks) and abdomen circumference (22 weeks). During intrauterine growth, all traits show a progressive increase in interindividual variability, which is more prominent for abdomen circumference.
  
  
  CONCLUSIONS
  The mathematical model applied to a large sample of growth profiles provided a satisfactory description of the individual fetal development and its biological variability, and allowed the construction of longitudinal distance standards useful for clinical purposes.
authors.affiliation: Pediatric Department, Institute G. Gaslini, University of Genova, Genoa, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Di Battista
authors.forename: E
authors.initials: E
authors.lastname: Bertino
authors.forename: L
authors.initials: L
authors.lastname: Benso
authors.forename: C
authors.initials: C
authors.lastname: Fabris
authors.forename: G
authors.initials: G
authors.lastname: Aicardi
authors.forename: M
authors.initials: M
authors.lastname: Pagliano
authors.forename: A
authors.initials: A
authors.lastname: Bossi
authors.forename: P
authors.initials: P
authors.lastname: De Biasio
authors.forename: S
authors.initials: S
authors.lastname: Milani
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging / Q000196:embryology; D005314:Embryonic and Fetal Development; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000196:embryology; D006257:Head / Q000000981:diagnostic imaging / Q000196:embryology; D006801:Humans; D008137:Longitudinal Studies; D011247:Pregnancy; D012016:Reference Values; D016216:Ultrasonography, Prenatal