title: Longitudinal blood flow in shared (arteriovenous anastomoses) and non-shared cotyledons in monochorionic placentae.
abstract: OBJECTIVE
  In this study we aimed to quantitate monochorionic twin placental blood flow in vivo through arterio-venous anastomoses (AVA) and corresponding vessels within normal cotyledons.
  
  
  METHODS
  The topography of chorionic plate vasculature was mapped using colour Doppler in ten monochorionic diamniotic twin (MCDA) pregnancies. Cotyledonary flow was derived by insonation of chorionic veins draining normal (n=10) and paired control shared cotyledons (n=10). Venous volume flow was calculated from five determinations of vessel diameter and three of time average mean velocity (TAMV). Measurements were repeated every 2-4 weeks from 18 until 32 weeks' gestation.
  
  
  RESULTS
  Blood flow through non-shared and shared cotyledons increased with gestation (p<0.0001). Median flow at 28 weeks through shared cotyledons was 16 ml/min (15-21) (median, interquartile range), lower than in shared cotyledons (31, 25-35) (p<0.001), as was median volume flow across gestation calculated as area under the curve (shared cotyledons 126 (122-167), control cotyledons 269 (214-274), p=0.01). However, velocity was similar, with the difference due to smaller vein diameters draining shared compared to normal cotyledons (mean 3.6mm (SD 0.8) vs. 4.5mm (0.8), p=0.004). Ex vivo quantitation of insonated cotyledons and of all cotyledons confirmed the difference in vein diameter in the placentae studied.
  
  
  CONCLUSIONS
  Blood flow through shared cotyledons was lower across gestation than through paired normal cotyledons in the placenta studied due to the smaller diameter of the AVA vessels. The size of AVAs rather than simply their presence and direction may contribute to determining transfusional imbalance in monochorionic twins.
authors.affiliation: Experimental Fetal Medicine Group, Institute of Reproductive and Developmental Biology, Imperial College London, Hammersmith Campus, London, UK. ling.wee@uclh.org <ling.wee@uclh.org>
authors.forename: L Y
authors.initials: LY
authors.lastname: Wee
authors.forename: M
authors.initials: M
authors.lastname: Sullivan
authors.forename: K
authors.initials: K
authors.lastname: Humphries
authors.forename: N M
authors.initials: NM
authors.lastname: Fisk
mesh_terms: D001163:Arteriovenous Anastomosis / Q000502:physiology*; D001783:Blood Flow Velocity; D002823:Chorion / Q000098:blood supply / Q000502:physiology; D018548:Cotyledon / Q000502:physiology*; D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D006801:Humans; D010920:Placenta / Q000098:blood supply*; D011247:Pregnancy; D016216:Ultrasonography, Prenatal