title: Second- and third-trimester ultrasound evaluation of chorionicity and amnionicity in twin pregnancy. A simple algorithm.
abstract: OBJECTIVE
  To develop a simple and systematic algorithm to determine chorionicity and amnionicity in the second and third trimester by ultrasound.
  
  
  METHODS
  The algorithm was constructed based upon years of experience in examining multifetal pregnancies and by adopting the different sonographic signs suggested in the literature.
  
  
  RESULTS
  The following parameters were used to construct the algorithm: sexing of the fetuses, placental location, and origin, thickness and number of layers of the membranes.
  
  
  CONCLUSIONS
  The flow chart developed is simple to use and embodies all possible sonographic parameters to help determine chorionicity and amnionicity in the second and third trimester.
authors.affiliation: Bellevue Hospital, New York, New York, USA. ana.monteagudo@med.nyu.edu
authors.forename: A
authors.initials: A
authors.lastname: Monteagudo
authors.forename: I E
authors.initials: IE
authors.lastname: Timor-Tritsch
mesh_terms: D000465:Algorithms; D000650:Amnion / Q000000981:diagnostic imaging*; D002823:Chorion / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011272:Pregnancy, Multiple; D014427:Twins; D016216:Ultrasonography, Prenatal