You aren't using the term, but it sounds like what I had while pregnant with my first. It's called absent end diastolic flow and/or reverse end diastolic flow. Have they used these terms? Have they done a Doppler ultra sound?
In my case, they were monitoring me as high risk already so I had a Doppler US at 26 weeks. this is able to measure the blood flow to/from fetus and mother. I showed the beginnings of AEDF. So as you mentioned, was put on "watch". I came back the next week and it was progressing. Eventually at 28 weeks I was put on bi weekly monitoring and told to be ready anytime to be sent to the hospital. Week 29 I was sent to the hospital directly from the doctors office as it was now REDF.
After 2 doses of steroid shots, they held off delivering and we were able to get 10 days more- all spent in the ICU hooked up to 24-7 monitoring....then her heart rate dropped 2x down in the 30s and they made the call to deliver. Funny how someone mentioned the umbilical cord falling off- the NICU nurse told me hers was the size of a pencil and just fell off too. I never saw it.
She was early and tiny (3lbs) but all else was perfect. And I know have a 2 1/2 yr old that is thriving with no issues at all. She's taller and talks more than any of her peers.
It's very scary! Ask to be monitored frequently. Ask for the Doppler US. Sounds like they are on top of it. Good luck and if you have any questions let me know.
I'm interested in hearing about all the reasons why though- since mine was never diagnosed and now I'm pregnant again....