I had this - was only just above the line on the graph but was still advised could go into labour early, risk of cord prolapse and PPH etc...
Wasn't offered an early induction (would have refused anyway), went into labour naturally 2 weeks late. Waters went during a VE and there was a lot!
Labour was long (2 days) as the extra fluid meant my daughter never fully engaged so there wasn't enough pressure on cervix to dilate at a decent speed.
Ended up with forceps delivery under epidural as she had turned into an awkward position during the labour (consultant reckons this was because the fluid levels allowed her freedom of movement). I pushed her out myself but the forceps were needed to rotate her as she came down to allow her head and shoulders to come out.
I did have an episiotomy and a third degree tear, and lost a fair amount of blood but this was prob due to forceps rather than extra fluid as my bump wasn't particularly huge.
My daughter did need help to breathe on arrival and was thoroughly checked over by the neonatologists for a couple of hours after birth, but this was nothing to do with the extra fluid, more the trauma of a forceps delivery after a very long labour.
One thing to bear in mind which I wish I'd known - if you're hoping to remain active during your labour you may have a fight on your hands to stay off the continuous monitoring machine - they like to put ladies who have extra fluid on this I'm told because it's the quickest way of them knowing if the cord has come down. This had a big effect on how I dealt with my labour as I'd banked on being active...
When you have your ultrasound they'll be able to measure the pools of fluid to work out how much 'extra' over the norm you have and will thoroughly check the baby for any abnormalities - although 90% of the time these would have been picked up at earlier scans. The only one they can't really check for on the ultrasound is a blockage in the baby's oesophogus so your consultant will probably recommend the 'tube down the throat' check at birth which is very quick indeed.
Have you been checked for gestational diabetes? This can cause extra fluid, and I was checked for it when my excess fluid was picked up. Didn't have it though - I think a large number of cases of polyhydramnios are incidental and no cause is ever found. Try not to worry yourself about it and DON'T Google... there are some scary and VERY rare complications associated with it which just aren't worth worrying yourself with. Most of these exceptional cases are those who have had excess fluid from early on in the pregnancy rather than those who have it picked up toward the end.
Sorry I've rambled a bit, hope this makes sense!