title: Transmitted arterio-arterial anastomosis waveforms causing cyclically intermittent absent/reversed end-diastolic umbilical artery flow in monochorionic twins.
abstract: OBJECTIVE
  To characterize the phenomenon of retrograde transmission of arterio-arterial anastomosis (AAA) interference patterns on umbilical artery (UA) waveform by (a) documenting the periodicity, (b) correlation with in vivo and in vitro demonstration of AAAs and (c) reproducing these patterns by computer modelling.
  
  
  METHODS
  Monochorionic twins (MC) twins underwent placental and umbilical Doppler studies. AAAs were sought by pulse wave Doppler of their bi-directional interference pattern and confirmed by postnatal injection studies. The periodicity of transmitted patterns in the UA was determined. Determinants of the transmitted patterns were ascertained by computer modelling of physiological and fetal variables.
  
  
  RESULTS
  Among 83 prospectively studied MC twin pregnancies; a transmitted pattern was observed in 6 (7 per cent) patients for 15-114 days. This was found in 20 per cent (6/30) of smaller MC twins discordant for growth restriction but in no appropriately grown twins. It was only observed in association with AAAs validated both in vivo and in ex vivo. Computer modelling demonstrated that this pattern could be reproduced by summating end diastolic flow with a high pulsatility index in the UA in the presence of a large AAA. Consistent with this, MC twins with a transmitted pattern had larger AAAs (median diameter 4.3 mm interquartile range 4.1-5.2) compared to MC twins discordant for intrauterine growth restriction (2.1 mm interquartile range 1.5 to 2.8) (P<0.05) without a transmitted pattern. Perinatal mortality was similar in the fetuses with and without transmitted patterns (0/12 vs. 2/48 P=0.7).
authors.affiliation: Centre for Fetal Care, Queen Charlotte's and Chelsea Hospital and Institute of Reproductive and Developmental Biology, Imperial College London, Hammersmith Campus, Du Cane Road, W12 0NN, London, UK. l.wee@imperial.ac.uk
authors.forename: L Y
authors.initials: LY
authors.lastname: Wee
authors.forename: M J
authors.initials: MJ
authors.lastname: Taylor
authors.forename: T
authors.initials: T
authors.lastname: Vanderheyden
authors.forename: D
authors.initials: D
authors.lastname: Talbert
authors.forename: N M
authors.initials: NM
authors.lastname: Fisk
mesh_terms: D000328:Adult; D001159:Arterio-Arterial Fistula / Q000000981:diagnostic imaging* / Q000196:embryology; D001783:Blood Flow Velocity; D003198:Computer Simulation; D003971:Diastole; D004200:Diseases in Twins; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005330:Fetofetal Transfusion / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D008954:Models, Biological; D011247:Pregnancy; D011446:Prospective Studies; D014430:Twins, Monozygotic; D018615:Ultrasonography, Doppler, Color; D016216:Ultrasonography, Prenatal; D014469:Umbilical Arteries / Q000000981:diagnostic imaging / Q000196:embryology / Q000503:physiopathology*