The Significance of Yolk Sac Number in Monoamniotic Twins

Abstract

Background: Detection of a single yolk sac on early first trimester ultrasound was previously thought to be a reliable diagnostic feature of monochorionic monoamniotic (MCMA) twin pregnancies. Objectives: To determine the frequency of two yolk sacs in MCMA twin pregnancies and the association of yolk sac number with pregnancy outcomes. Methods: A retrospective cohort analysis of MCMA twins managed at a tertiary obstetric centre from January 2003 until February 2017. All MCMA twin pregnancies were diagnosed on tertiary centre ultrasound and, where possible, placental histopathology postnatally. All MCMA twin pregnancies, including conjoined twins, with available first trimester ultrasounds fr..