Hi There

I had grade 4 as well... mine was like yours & completely covering.. it stayed posterior which was lucky!

I had absolutely no signs of bleeding up until 32 weeks... got out of the shower one night to put my clothes on & its just started... massive gush
It went for about 40 mins on and off, I was taken to hospital, and then rushed via ambulance to a different hospital that had the facilities to deal with a 32 week old bubba in NICU.
Luckily, the bleeding stopped, they kept me in for 2 weeks (I had small spots of old blood) - and let me out at 34 weeks to go home on bed rest only.
I was home for a week, and at 35 weeks, had another bleed, so was taken to hospital again. It took longer to stop that time, but it was minimal enough to monitor.... I ended up holding on until 36 weeks where I had a c/s.

My FS said with the grade that I had, it was very rare that I didn't have any bleeding until 32 weeks, he said it was more common to have bleeding (even if it's just spotting) from 28 weeks onwards.

My advice would be to take it easy (do as little as possible!) - and definately have the household organised to be without you for a few weeks!
The only other thing I can say is that you need to get to a hospital or phone them at the very least at ANY sign of bleeding at all.
My FS wanted to have me in hospital from 30 weeks on, but for us it just wasn't possible... look after yourself