title: Umbilical and fetal middle cerebral artery Doppler reference ranges in a twin population followed longitudinally from 24 to 38 weeks' gestation.
abstract: OBJECTIVE
  To construct monochorionic diamniotic (MCDA) and dichorionic diamniotic (DCDA) twin reference ranges for umbilical artery (UA) pulsatility index (PI), UA resistance index (RI), fetal middle cerebral artery (MCA) PI and peak systolic velocity (PSV) and cerebroplacental ratio (CPR) from 24 weeks' to 38 weeks' gestation and compare these with published normal values for singleton pregnancies.
  
  
  METHODS
  This prospective multicenter cohort study included 1028 unselected twin pairs recruited over a 2-year period. Participants with dichorionic twins underwent fortnightly ultrasound surveillance from 24 weeks' gestation, with monochorionic twins being followed every 2 weeks from 16 weeks until delivery. A total of 7536 fetal Doppler examinations in 618 twin pregnancies were included in the analysis, with reference ranges for MCDA and DCDA pregnancies constructed for each of the Doppler indices using multilevel modeling.
  
  
  RESULTS
  UA-PI and UA-RI appear to be higher in twins than in singletons, and MCA-PI and MCA-PSV appear to be lower. The CPR also appears to be lower in twins than in singletons. Similar MCA indices were observed in MCDA and DCDA twins.
  
  
  CONCLUSIONS
  We have established longitudinal reference ranges for UA-PI and UA-RI, MCA-PI and MCA-PSV and CPR in twin pregnancies, which appear to differ from those in singleton pregnancies. The derived twin-specific reference ranges may be more appropriate in the surveillance of these high-risk pregnancies. Applying the singleton CPR cut-off of ≤ 1.0 may lead to a large number of false-positive diagnoses of cerebral redistribution in twin fetuses.
authors.affiliation: National Maternity Hospital, Dublin, Ireland.
authors.forename: C
authors.initials: C
authors.lastname: Mulcahy
authors.forename: F M
authors.initials: FM
authors.lastname: McAuliffe
authors.forename: F
authors.initials: F
authors.lastname: Breathnach
authors.forename: M
authors.initials: M
authors.lastname: Geary
authors.forename: S
authors.initials: S
authors.lastname: Daly
authors.forename: J
authors.initials: J
authors.lastname: Higgins
authors.forename: A
authors.initials: A
authors.lastname: Hunter
authors.forename: J
authors.initials: J
authors.lastname: Morrison
authors.forename: G
authors.initials: G
authors.lastname: Burke
authors.forename: S
authors.initials: S
authors.lastname: Higgins
authors.forename: P
authors.initials: P
authors.lastname: Dicker
authors.forename: R
authors.initials: R
authors.lastname: Mahony
authors.forename: E
authors.initials: E
authors.lastname: Tully
authors.forename: F
authors.initials: F
authors.lastname: Malone
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D015331:Cohort Studies; D005260:Female; D005317:Fetal Growth Retardation / Q000000981:diagnostic imaging; D005333:Fetus / Q000098:blood supply; D005865:Gestational Age; D006801:Humans; D008137:Longitudinal Studies; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging*; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D011446:Prospective Studies; D016032:Randomized Controlled Trials as Topic; D012016:Reference Values; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D016216:Ultrasonography, Prenatal; D014469:Umbilical Arteries / Q000000981:diagnostic imaging*
keywords: Doppler ultrasound; middle cerebral artery; twin reference ranges; umbilical artery