What would PAIF do?

ale_nicu_rn

Backstory: FET on 2/5, BFP on 2/14. Betas in siggy doubled well. First u/s at 6w5d showed empty sac. Repeat u/s today at 7w4d showed empty sac again. Beta today was 16546. Doubling time of 104 hours Doc says probably not viable and to stop meds and wait for m/c or schedule d and c. He offered another u/s if I want. I feel a little crampy today, but no bleeding at all. Would my beta still be rising appropriately if there was no chance of viability?