A double gestational sac generally represents the presence of two gestational sacs in the uterine cavity for a twin pregnancy. Normally, a woman’s discharged egg and sperm combine to form a fertilized egg, which develops into a gestational sac after it has been deposited. The gestational sac is the primitive placental tissue, a small embryo wrapped in amniotic membrane and a network of blood vessels, which is the initial form of pregnancy. Dual gestational sacs are the simultaneous presence of two gestational sacs in the uterus during a single pregnancy. It consists of two oocytes fertilized at the same time, forming two fertilized eggs that develop into a fetus at the same time. Twin pregnancies can be categorized into two types: monozygotic and dizygotic. Monozygotic twins are one fertilized egg that forms two placentas, each developing into a fetus with the same genes. A dizygotic twin pregnancy is one in which two eggs are fertilized with sperm separately to form a fertilized egg, each of which is not genetically identical. Pregnant women with twin pregnancies should take folic acid regularly during the first trimester of pregnancy, strengthen pregnancy monitoring, and undergo regular maternity checkups.