Thanks for your query.
Generally, a gestational sac
greater than 16 mm with no visible fetal pole
signifies a failed pregnancy
ALso, with your previous history of ectopic pregnancy, there should be thorough scanning of adnexa for ectopic pregnancy again.
In order to be completely sure, please go for a blood B - HCG
estimation, which would surely differentiate between an ongoing viable intrauterine pregnancy and other possibilities.
ALso, one more option is to rescan after a few days, when still, if the fetal pole is not visible, it is definitely a failed pregnancy.
All the best.