Me me me me me! 
But judging from when I have posted about this, no-one else.
My experience: ttc, became pg within a couple of months. 12wk scan fine. At 20 wks the sonographer spotted what he said was an 'amniotic band'. He pointed out what looked like a band running across one corner of my uterus, creating a little en-suite section. He didn't seem overly concerned but said it could cause growth problems in the baby and referred me for an extra scan at 31 wks. (norm is to only have 2 scans, at wk 12 and wk 20.)
Cue googling... panicking etc! If you google amniotic band, it is rare but usually happens in women who have had uterine surgery in the past, eg an abortion. From my understanding, it's sort of a sticky long fibre attached to each side of the uterus, and if the baby's limbs touch it, there's a possibility of threads of the band coming off and wrapping round limbs, causing serious problems. Scary stuff! Anyway when I was googling this, it didn't ring quite right with the single band shown in my uterus. One site (Babycentre I think) said that often docs call it an amniotic band when they mean an amniotic sheet, which is sort of a fold in the fluid that solidifies. That is apparently more common, and not harmful to the baby. So I decided that's what I had. Baby was also breech, standing up, at the 20wk scan.
Roll on to the 31wk scan: I knew baby was still breech as his head hadn't really moved from the top left of my uterus (band thing blocking off top right). He confirmed this at the scan, and said that the band was no longer an issue as when baby had grown, the band had been pushed against the wall of the uterus so out of the way. Cue relief!
Was then booked in for a scan at 35 weeks due to breech position of baby (usually means c-section necessary, but most babies turn of their own accord before 35 wks).
Again I knew he was still breech. At 35 wk scan, the band was really, really clear even to me and DH and the sonographer couldn't get all the measurements he needed - he couldn't see the hands. Cue mad panic and a referral for a more specialist scan and sonographer at Kings in London. At this scan (3 days ago!) he got all the measurements including hands (phew) and got a consultant in.
I could have kissed the consultant: she was so kind and knowledgeable! She said I'd been incorrectly diagnosed with the amniotic band, that due to my history (no uterine surgery) and the nature of the fibre, it was actually a permanent septum in my uterus, a congenital defect basically. The good news is that it doesn't affect the baby at all apart from having slightly less space. She said it was the reason my baby is breech, and that future pregnancies are likely to be breech too.
The consultant at my usual hospital had wanted to do an ECV (where you lie flat, and they try to turn the baby to a head-down position manually by putting hands on your tummy) and this would not have worked due to restricted space, and potentially been dangerous for baby. my instincts had told me to decline the ECV anyway but I felt like I was being a diva!
So I'm being booked in for an elective c-section in a fortnight, when I'll be 39 weeks 
Anyway, Kings is the largest fetal medicine unit in Europe according to the angel-lady consultant I saw there, and they only see 2-3 cases of uterine septum each year. So if you can get down there for a scan and to see her, I would strongly recommend it. She told me to come back a few months post-pregnancy for a scan to look at it, but it obviously didn't cause any problems with me getting or staying pregnant, so unlikely to be an issue in the future - except for baby probably being breech again so probably no natural deliveries for me.
In your case - hope my (long, sorry! 
) story helps a little in case you have similar difficulties with midwives and consultants being unfamiliar with it. I think it will depend how much space is restricted by the septum - I'd estimate mine cuts off about 20%.
On the bright side, angel consultant lady said there are loads of different congenital uterine defects and a septum is really, really not serious I think they can operate if it looks like it will be a problem, but I can't urge you strongly enough to get yourself a referral to Kings in London for specialist advice.
Sorry for mammoth post! just excited to find someone else with this! x