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                                                             If you are past seven weeks pregnant, seeing no heartbeat might be a sign of 
miscarriage -- but it may not be definite. In early 
pregnancy, being off by a few days with your estimated last menstrual period -- or having an irregular ovulation pattern -- can make a difference in whether or not you should see a heartbeat on the 
ultrasound. For example, if you did not ovulate exactly two weeks after your menstrual period started, there is a chance you are not really "seven weeks pregnant" in 
gestational age even if it has been seven weeks since your last menstrual period. In this situation, unless your doctor has other evidence to make a firm diagnosis, you will probably be asked to wait a week and come in for another ultrasound.
Sometimes a lack of a fetal heartbeat does definitely indicate miscarriage, however. These situations would include:
    Having previously seen the heartbeat but finding no heartbeat on a subsequent ultrasound
    Seeing no heartbeat and having falling 
hCG levels
    Having a followup ultrasound after a week and detecting no change
    Having other ultrasound measurements that indicate a heartbeat should definitely be present
I hope you are satisfied with the answer
take care.