Welcome to healthcare magic,
At six weeks /16 mm gestational sac
usually fetal pole
is seen. Even on the repeat scan after one week if fetal pole is not seen it could be blighted ovum
or an embryonic pregnancy. The time taken for spontaneous miscarriage
is variable from person to person. If next week's scan is showing blighted ovum you may go for medical termination or D & C if you are not keen on waiting.
Hope this helped,