A: Congratulations, Autumn. Your last ultrasound suggests you're doing a great job nourishing your growing babies! As you know, with a twin gestation your overall uterine size doesn't provide details about the individual growth of your babies. Most health providers will order ultrasounds multiple times during a twin pregnancy to assess how each baby is growing. Often, an ultrasound is performed every four to six weeks if the babies are growing at a similar rate. If there is a concern about fetal development, the quantity of amniotic fluid around the babies, or if the babies are growing at different rates, ultrasound may be used more frequently. Toward the end of your pregnancy, the position of each baby becomes more important. This will help your provider decide whether a vaginal delivery is possible, or whether a cesarean section is necessary.