title: Ultrasound estimation of birth weight in twin pregnancy: comparison of biometry algorithms in the STORK multiple pregnancy cohort.
abstract: OBJECTIVE
  The aims of this study were first, to ascertain the accuracy of formulae for ultrasonographic birth-weight estimation in twin compared with singleton pregnancies and second, to assess the accuracy of sonographic examination in the prediction of birth-weight discordance in twin pregnancies.
  
  
  METHODS
  This was a retrospective cohort study including both singleton and twin pregnancies. Routine biometry was recorded and estimated fetal weight (EFW) calculated using 33 different formulae. Only pregnancies that delivered within 48 h of the ultrasound scan were included (4280 singleton and 586 twin fetuses). Differences between the EFW and actual birth weight (ABW) were assessed by percentage error, accuracy in predictions within ± 10% and ± 15% of error and use of the Bland-Altman method. The accuracy of prediction of the different cut-offs of birth-weight discordance in twin pregnancies was also assessed using the area under the receiver-operating characteristics curve (AUC).
  
  
  RESULTS
  The overall mean absolute percentage error was ≤ 10% for 25 formulae in singleton pregnancies compared with three formulae in twin pregnancies. The overall predictions within ± 10% and ± 15% of the ABW were 62.2% and 81.5% in singleton and 49.7% and 68.5% in twin pregnancies, respectively. When t e formulae were categorized according to the biometric parameters included, those based on a combination of head, abdomen and femur measurements showed the lowest mean absolute percentage error, in both singleton and twin pregnancies. The predictive accuracy for 25% birth-weight discordance using the Hadlock 2 formula, as assessed by the AUC, was 0.87.
  
  
  CONCLUSIONS
  Ultrasound estimation of birth weight is less accurate in twin than in singleton pregnancies. Formulae that include a combination of head, abdomen and femur measurements perform best in both singleton and twin pregnancies.
authors: Fetal Medicine Unit, Academic Department of Obstetrics and Gynaecology, St George's University of London, London, UK.
authors: A
authors: A
authors: Khalil
authors: F
authors: F
authors: D'Antonio
authors: T
authors: T
authors: Dias
authors: D
authors: D
authors: Cooper
authors: B
authors: B
authors: Thilaganathan
mesh_terms: D000465:Algorithms; D001699:Biometry / Q000379:methods*; D001724:Birth Weight / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D011237:Predictive Value of Tests; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000502:physiology*; D059285:Pregnancy, Twin / Q000502:physiology*; D012372:ROC Curve; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: algorithms; biometry; birth weight; formula; twin pregnancy; ultrasound