Low implantation...

adies I could really use your input... So last night I was in the er for the second time due to bleeding. They were able to see baby (measuring 6 weeks and 2 days), the heartbeat (122!), and hcg had gone up (from 5200 to over 20000 in 5 days). My cervix is closed. All good things, but the dr said that with the ultrasound they noticed the baby implanted low on the uterine wall. She said it made it a higher miscarriage risk, which of course is terrifying to hear. Have any of you ladies heard of this, or dealt with it?