A gestational sac with twins can be detected by ultrasound around 50-60 days after conception. A gestational sac if there are twins is generally referred to as identical twins, which is a condition in which one fertilized egg, produced by the union of one sperm and one egg, splits into two embryos during development. The two fetuses have nearly identical genetics, such as sex, chromosomal karyotype, and genes carried. Generally, counting from the first day of the last menstrual period, the gestational sac can enter the uterine cavity at around 50 days of pregnancy, but some gestational sacs enter the uterine cavity later, which may be around 60 days, therefore, an ultrasound can be used to determine if there are two buds in one sac on the 50th-60th day of pregnancy to determine twins. If identical twins are diagnosed, you should take care of your nutritional supplements during pregnancy and follow your doctor’s instructions for labor and delivery.