title: Difference in nuchal translucency between monozygotic and dizygotic spontaneously conceived twins.
abstract: OBJECTIVE
  To assess nuchal translucency (NT) thickness and differences in inter-twin NT thickness among naturally conceived monozygotic and dizygotic twins.
  
  
  METHODS
  Enrolled women prospectively underwent NT measurement for both twins between 11 and 14 weeks of gestational age. NT thickness and inter-twin NT difference were recorded and compared among dizygotic twins, monozygotic dichorionic twins, and monozygotic monochorionic twins.
  
  
  RESULTS
  This study obtained analyzable data for 174 monozygotic twins and 107 dizygotic twins. Of the 174 monozygotic twins, 105 were monochorionic, and 69 were dichorionic. Monozygotic monochorionic twin pregnancies had a significantly higher mean fetal NT thickness (1.48 +/- 0.62 mm) than either dizygotic twin pregnancies (1.34 +/- 0.50 mm) or monozygotic dichorionic twin pregnancies (1.31 +/- 0.48 mm). Mean inter-twin NT difference was significantly lower in monozygotic dichorionic twin pregnancies (0.37 +/- 0.19 mm) than in dizygotic twin pregnancies (0.57 +/- 0.22 mm) or monochorionic twin pregnancies (0.65 +/- 0.43 mm).Irrespective of twin zygosity, NT thickness and inter-twin NT difference were larger in monochorionic twins than in dichorionic twins (1.48 +/- 0.62 mm versus 1.33 +/- 0.49 mm, and 0.65 +/- 0.43 mm versus 0.49 +/- 0.23 mm, respectively).
  
  
  CONCLUSIONS
  During first-trimester ultrasonographic screening for Down syndrome, monochorionic twin pregnancies have the greatest NT thickness and monozygotic dichorionic twin pregnancies have the lowest inter-twin NT difference.
authors.affiliation: Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Linkou Medical Center, TaoYuan, Taiwan. pjcheng@cgmh.org.tw
authors.forename: Po-Jen
authors.initials: PJ
authors.lastname: Cheng
authors.forename: Shang-Yu
authors.initials: SY
authors.lastname: Huang
authors.forename: Sheng-Wen
authors.initials: SW
authors.lastname: Shaw
authors.forename: Ching-Hwa
authors.initials: CH
authors.lastname: Hsiao
authors.forename: Chuan-Chi
authors.initials: CC
authors.lastname: Kao
authors.forename: Ho-Yen
authors.initials: HY
authors.lastname: Chueh
authors.forename: T'sang-T'ang
authors.initials: TT
authors.lastname: Hsieh
mesh_terms: D000328:Adult; D004200:Diseases in Twins / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000235:genetics; D004314:Down Syndrome / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000235:genetics; D005260:Female; D005865:Gestational Age; D006801:Humans; D009333:Neck / Q000000981:diagnostic imaging / Q000196:embryology; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic