<prompt> Which of the following is true regarding chorionicity in multifetal pregnancyMonochorionic membranes should have four layersDichorionic pregnancies are always dizygoticMonochorionic pregnancies are always dizygoticChorionicity is accurately determined by first trimester ultrasound scan  <response>: Monochorionic pregnancies have dividing membrane that is 2 layer thick. Monozygous twins can be dichorionic as well. 