A gestational sac of 26mm x 13mm is about 6 weeks pregnant. Usually when a woman is in the early stages of pregnancy, she can approximate how long she is pregnant based on the size of the gestational sac. An ultrasound with a gestational sac of 26mm x 13mm is about 6 weeks pregnant. If you have regular menstrual cycles, you can usually see the fetal buds and primitive heart tube pulsation when you have an ultrasound at 6 weeks of pregnancy. If you don’t see any fetal buds and fetal heart tube pulsations, you can wait a few more days for a follow-up ultrasound. Generally, when a woman is about 6 weeks pregnant, due to changes in hormone levels in the body, she is prone to symptoms of early pregnancy reactions, such as nausea and vomiting, breast swelling and pain, body fatigue, dizziness, drowsiness, and so on, and pay attention to more rest in early pregnancy.