title: Sonographic evaluation of fetal growth: growth rate variability as a function of the interval between examinations.
abstract: OBJECTIVE
  Fetal growth rates determined on the basis of findings at two separate sonographic examinations can be used to detect growth abnormalities. This article determines the relationship between the length of the interval between examinations and the associated variability in measured fetal growth rates.
  
  
  METHODS
  We analyzed 1479 fetal measurements of the biparietal diameter, average abdominal diameter, and femur length from 539 normal pregnancies. Mean growth rates were computed as functions of gestational age. The standard deviation of the growth rate was computed as a function of the interval between examinations.
  
  
  RESULTS
  The standard deviation of fetal growth rates is relatively constant when the interval between examinations is 8-10 weeks or more, but increases substantially when the interval is fewer than 6 weeks.
  
  
  CONCLUSIONS
  From a purely statistical point of view, the optimal interval for assessment of fetal growth rates is 8-10 weeks or more. Shorter intervals, however, usually are mandated by the clinical situation. Correction factors can be used to determine the standard deviations and associated confidence intervals for fetal growth measured over a period of fewer than 10 weeks.
authors.affiliation: Department of Radiology, Jefferson Medical College of Thomas Jefferson University Hospital, Philadelphia, PA 19107-5244.
authors.forename: E J
authors.initials: EJ
authors.lastname: Halpern
authors.forename: L N
authors.initials: LN
authors.lastname: Nazarian
authors.forename: L
authors.initials: L
authors.lastname: Needleman
authors.forename: W W
authors.initials: WW
authors.lastname: Hauck
authors.forename: A B
authors.initials: AB
authors.lastname: Kurtz
mesh_terms: D005314:Embryonic and Fetal Development; D005260:Female; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D013997:Time Factors; D016216:Ultrasonography, Prenatal