Role of Ultrasound in the Determination of Chorionicity of Twin Pregnancies : How Accurate is Intertwin Membrane?

Abstract

Background: Prenatal determination of chorionicity by ultrasound has helped in bringing down the perinatal morbidity and mortality in twin pregnancies. In this study, the role of intertwin membrane thickness as a marker for ultrasound determination of chorionicity is being considered.

Materials & Methods: Antenatal chorionicity of twin pregnancies was determined using thickness of intertwin membrane as criteria in ultrasound. The gestational age at the time of assessment was documented. Postnatal confirmation of chorionicity was made by placental examination and compared with ultrasound chorionicity.

Results: Chorionicity was correctly determined in 92.9% of dichorionic twins and 71.4% of monochorionic twins when intertwin membrane thickness was taken as criteria. Also, when the chorionicity was assessed before 12 weeks, the accuracy was found to be greater.

Conclusions: Ultrasound assessment of chorionicity based on thickness of intertwin membrane is more accurate for dichorionic than monochorionic twin pregnancies. There is higher accuracy if ultrasound is performed in the first trimester.