Measuring Earlier & Slow Heartbeat

Hi ladies - any insight would be much appreciated. Hubby and I just came back from our first normally scheduled US and we should be measuring at 8 weeks. We ended up measuring at 6 weeks and 1 day. We had an emergency US on the 28th due to spotting and doctor said we measured at 5 weeks 4 days. Baby has grown since that first US, but should have grown more per the doctor.

We saw the heartbeat flickering on the screen today, but couldn't hear it... and doctor said it was slower than normal. We are scheduled for another US next week in hopes that the heartbeat gets stronger, but doctor says we are 50/50 in terms a viable pregnancy at this point and she did not sound positive 😔 has anyone had a similar situation and gone on to have a healthy pregnancy?