If the usual menstrual cycle is once every 30 days and the blood HCG or urine HCG test is positive at 43 days of menopause, but no gestational sac is seen through ultrasound, it may be due to the following reasons: 1. Ovulation is pushed back, when the pregnancy is still relatively short and the location of the gestational sac cannot be found yet through ultrasound, and in the absence of discomfort, another ultrasound test can be done at an interval of 5 days. It is also recommended to rule out the possibility of ectopic pregnancy by monitoring the blood HCG. If the blood HCG is able to double up every other day, it indicates a high probability of intrauterine pregnancy. If it does not double up and only rises a little, it may be an ectopic pregnancy.2. It may be due to an ectopic pregnancy and further tests are needed to make a preliminary diagnosis.