••• Chapter 16^ First Trimester Ultrasound^175
❍ How would you describe the amnionicity and chorionicity of this first trimester pregnancy?
Monochorionic and triamniotic.❍ How are the number of yolk sacs and amnionicity related?
The number of yolk sacs equals the number of amniotic sacs.
❍ What is the chance of delivering twins if two gestational sacs are seen on early US studies?
57%.
❍ What does this percentage increase to if two embryonic poles with cardiac activity are visualized?
87%.
❍ When is the best time to determine amnionicity and chorionicity in a multiple gestation?
8 to 10 weeks (the earlier the better).
❍ What structure are the arrows pointing to in the ultrasound images?
Corpus luteum cysts.