Journal of Ultrasound in Medicine, Vol 7, Issue 6 327-332, Copyright © 1988 by American Institute of Ultrasound in Medicine
Membrane thickness in ultrasound prediction of chorionicity of twin gestations
R. R. Townsend, G. F. Simpson and R. A. Filly
Department of Radiology, University of California School of Medicine, San Francisco.
A retrospective review of sonograms performed on 75 twin gestations was
performed to evaluate the ability of sonography to distinguish
monochorionic from dichorionic gestations based on the thickness of the
membrane separating the fetuses. Clinical or pathologic evidence of
chorionicity and amnionicity was available in all cases. A thick membrane
had a predictive value of 83% for dichorionicity and was seen in 89% of the
first sonograms obtained on dichorionic gestations. Of third trimester
dichorionic pregnancies, a thick membrane was seen in only 52%. A thin
membrane on the initial study had a predictive value for monochorionic
diamniotic pregnancy of 83%, but was seen in only 54% of cases. There was
100% intraobserver and 91% interobserver concordance in interpretation of
membrane thickness. Technical factors important in interpretation of
membrane thickness are discussed. The appearance of the membrane can be
useful in sonographic evaluation of chorionicity and amnionicity in twin
gestations, but should be used in conjunction with all other information
available.
