Twin Fetal Development A Closer Look At Your Developing Babies The test is typically administered between 2428 weeks gestation Gestational Diabetes (GDM) occurs in 36% of twin pregnancies Twin gestations are screened for GDM using the same challenge (50g glucose load), the same schedule (2428 weeks of gestation), and the same normal ranges that are used for singleton gestations If twins are visible at your 12week ultrasound, the sonographer will perform a chorionicity scan to determine if the twins share a placenta Twins who share a placenta are called monochorionic 24 weeks pregnant with twins ultrasound