This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Which of the following is true regarding chorionicity in multifetal pregnancy 
Select and explain. 
A. Monochorionic membranes should have four layers, B. Dichorionic pregnancies are always dizygotic, C. Monochorionic pregnancies are always dizygotic, D. Chorionicity is accurately determined by first trimester ultrasound scan
D: Chorionicity is accurately determined by first trimester ultrasound scan
Answer: D: Chorionicity is accurately determined by first trimester ultrasound scan 
Explanation: Monochorionic pregnancies have dividing membrane that is 2 layer thick. Monozygous twins can be dichorionic as well.