Twins a small one is the cause of pregnancy after the sac of the nutrient absorption is not the same caused by the baby grows up, the fetal absorption of nutrients is not the same, will also cause a big one a phenomenon, this is a normal phenomenon, pregnant women pay attention to strengthen the dietary nutrients, at the same time recommended reasonable supplementation of trace elements, can promote the development of the baby. The best pregnancy regular maternity check to see the development of the fetus, as long as the difference between the two babies is not too big do not worry, if the difference is too big may be the small baby dysplasia, may be caused by congenital diseases, it is best to go to the hospital to do the Down’s syndrome, four-dimensional ultrasound examination to rule out fetal malformations. Note that pregnant twins in pregnancy will appear transfusion syndrome, if there is a transfusion syndrome will cause a large and a small, if through the examination to rule out this situation, the two babies have a certain difference do not worry too much.