If you have a blood test and you cannot see the gestational sac on the ultrasound, it is possible that the pregnancy is relatively recent or that the pregnancy is ectopic. However, it depends on the exact time of pregnancy to determine if the gestational sac can be seen. In general, if the menstruation is very regular, within 35 days of menopause, you will not be able to see the gestational sac; if you have an abdominal ultrasound, you will not be able to see the gestational sac within 40 days, which is normal. If the gestational sac is still not visible after 40 days, or if the gestational sac is not visible even after 35 days during the ultrasound, it is highly suspected that the pregnancy is ectopic and further examination is needed to check the chorionic gonadotropin in the blood. If you have an ectopic pregnancy, you need to be treated as soon as possible.