Pregnancy can not find the gestational sac, low progesterone may be related to the shorter time of conception, but also need to be vigilant about ectopic pregnancy. Generally after 5 to 6 weeks of pregnancy for ultrasound examination can observe the gestational sac, if the time of conception is too short for ultrasound generally can not find the gestational sac, you can carry out blood HCG first to clarify whether the pregnancy. If pregnant, can be observed for a period of time for ultrasound review. If the pregnancy time is longer and still can not observe the gestational sac and progesterone is low, should be alert for ectopic pregnancy. Ultrasound is recommended to check for gestational sacs in pelvic areas other than the uterine cavity. If the pregnancy is ectopic, the blood HCG value is usually low. Therefore, if you cannot find a gestational sac after pregnancy, you can observe it first. If the absence of gestational sac persists, ectopic pregnancy should be suspected and treatment should be taken proactively.