title: Reference ranges for the pulsatility index of the fetal aortic isthmus in singleton and twin pregnancies.
abstract: OBJECTIVE
  The purpose of this study was to estimate reference ranges for the pulsatility index (PI) of the fetal aortic isthmus in uncomplicated singleton and twin pregnancies during the second half of pregnancy.
  
  
  METHODS
  We conducted a cross-sectional observational study involving 543 healthy fetuses: 361 singleton pregnancies and 182 twin pregnancies between 19 and 36 weeks' gestation. The aortic isthmus PI was measured in 2 sonographic planes: the longitudinal aortic arch view and the 3-vessel and trachea view. We evaluated the reproducibility of aortic isthmus PI measurements between these planes by calculating intraclass correlation coefficients and limits of agreement. Scans were performed by 2 physicians, and intraobserver agreement was also measured. Regression analysis was used to estimate gestational age reference values for the aortic isthmus PI.
  
  
  RESULTS
  The aortic isthmus PI was significantly correlated with gestational age in singletons and twins during the second half of pregnancy (P < .01). We did not find significant differences between reference ranges in singletons and twins or between the sonographic views.
  
  
  CONCLUSIONS
  This study offers reference ranges for the aortic isthmus PI during the second half of gestation in singleton and twin pregnancies. Mean aortic isthmus PI values were similar in both types of gestations as well as both sonographic views. The aortic isthmus PI may be reliably obtained from either sonographic view.
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: Francisco
authors: F
authors: Gámez
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: María José
authors: MJ
authors: Rodríguez
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: José María
authors: JM
authors: Tenías
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: Javier
authors: J
authors: García
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: Pilar
authors: P
authors: Pintado
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: Raquel
authors: R
authors: Martín
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: Ricardo
authors: R
authors: Pérez
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain.
authors: Luis
authors: L
authors: Ortiz-Quintana
authors: Department of Obstetrics and Gynecology, Hospital General Universitario Gregorio Marañón, Universidad Complutense de Madrid, Madrid, Spain (F.G., P.P., R.M., R.P., L.O.-Q., J.D.L.-L.); and Department of Obstetrics and Gynecology (M.J.R., J.G.) and Research Support Unit (J.M.T.), Hospital la Mancha Centro, Alcázar de San Juan, Ciudad Real, Spain. jdeleonluis@yahoo.es.
authors: Juan
authors: J
authors: De León-Luis
mesh_terms: D001013:Aorta, Thoracic / Q000000981:diagnostic imaging* / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D059285:Pregnancy, Twin; D011674:Pulse; D012016:Reference Values; D016216:Ultrasonography, Prenatal
keywords: Doppler sonography; fetal aortic isthmus; nomograms; obstetric ultrasound; twin pregnancies