I was diagnosed with polyhydramnious at 34 weeks. The midwife at a routine appointment had measured me as being 43 weeks so I was sent for a scan and that's when it was diagnosed. I had all the tests for glucose, diabetes etc (can't remember all the tests/details as it was 13 years ago). All came back negative. At 35 weeks I had the steroid injection for baby's lungs. It wasn't too bad but I was very red the next day.
At 36 weeks I was admitted for hospital bedrest as I was so HUGE - the midwife said it looked like I was carrying a twin pregnancy. I could hardly walk and all movement was a challenge. I didn't want to be away from my other children but I was glad I'd been admitted as when I had been told the risks associated with PH I was scared.
Google is NOT your friend right now - it's good for basic info & being prepared but it's also awash with horror stories that you just don't how reliable they are. You'll be monitored closely from now on, which is reassuring.
I was scheduled for a CS at 38 weeks, but I was struggling so much they brought it forward to 37 weeks - they wouldn't do it any earlier as then the baby would be classed as premature.
DD was 7lb 5oz when born, I do remember seeing a poor member of staff absolutely soaked with amniotic fluid in the operating theatre! They take baby away for tests straight away (I had been warned about this beforehand) I think they test the throat/swallowing/stomach? To see if baby has normal physical functions. No cause of PH was ever found, it was just 'one of those things'.
Good luck with everything, just rest as much as you can, let everybody else do everything for you! Talk to your midwife/consultant about any worries or questions you have, they'll be able to reassure you.