Difference in nuchal translucency between monozygotic and dizygotic spontaneously conceived twins

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 anion, 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 monochrionic twin Pregnancies had a significantly higher mean fetal NT thickness (1.48 +/- 0.62 mm) than either dizygotic twill pregnancies (1.34 +/- 0.50 nm) 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). Conclusion 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. Copyright (C) 2010 John Wiley, & Sons, Ltd.