title: Positive predictive value of suspected growth aberration in twin gestations.
abstract: OBJECTIVE
  Our purpose was to determine the positive predictive value of ultrasonographic surveillance for growth abnormalities in twin gestations as a function of gestational age.
  
  
  METHODS
  Women with twin gestations and delivery between January 1992 and March 1998 who had a 20- to 24-week sonogram with normal fetal anatomic findings and who had at least 1 sonogram showing abnormal growth were identified. Abnormal growth on ultrasonography was defined as an estimated fetal weight <10th percentile, abdominal circumference <5th percentile, or twin discordance (>20% difference in twin weights as a function of the heavier twin). Birth weights were then assessed for evidence of twin discordance or growth restriction.
  
  
  RESULTS
  The positive predictive value for the occurrence of a growth abnormality at birth, after an abnormal growth finding on ultrasonography at any time during gestation, was 47.7%. The positive predictive value was greatest (85%) when suspected growth restriction was first documented at 20 to 24 weeks of gestation and decreased with increasing gestational age. Even though sonograms were obtained at a mean interval of 4.4 +/- 2.0 weeks, those gestations with normal growth at 20 to 24 weeks had an elapsed time of 10.3 +/- 3.9 weeks until a growth abnormality was subsequently detected.
  
  
  CONCLUSIONS
  In twin gestations the positive predictive value of a sonogram for a growth abnormality at birth is significantly decreased after normal findings on a 20- to 24-week sonogram. This finding suggests that a routine 2- to 4-week interval between sonograms for all twin gestations may be unwarranted.
authors.affiliation: Section of Maternal-Fetal Medicine and the Department of Obstetrics and Gynecology, Northwestern Memorial Hospital, Northwestern University Medical School, Chicago, Illinois, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Grobman
authors.forename: B V
authors.initials: BV
authors.lastname: Parilla
mesh_terms: D004200:Diseases in Twins / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D005317:Fetal Growth Retardation / Q000175:diagnosis / Q000000981:diagnostic imaging*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D012307:Risk Factors; D013997:Time Factors; D016216:Ultrasonography, Prenatal / Q000379:methods