Lexi, my bmi with my first pregnancy was about 53 (size 24) you probably aren't half as big as me, but I'll tell you what it meant for me. I had to see the consultant, not just the mw's, I couldn't give birth in the midwife led unit ten minutes away or at home, I had to be in hospital. Also a waterbirth was out of the question.
I had to have a gestational diabetes test (They test your blood, you drink some lucozade, go sit somewhere for 2 hours, then go back for another blood test) which I passed fine. My blood pressure was perfect. No complications. The consultant was a cheerful chap who took joy in doing a LOT of scaremongering, predicted I'd end up with everything from diabetes to pre-eclampsia, a baby the size of a christmas turkey, and said I would most likely end up with a c section. So I had to go and see the anaesthesiologist who did a bit more scaremongering and telling off 
and disappointed prodding of back squidge. 
I had growth scans because obviously because I was fat the baby was going to be huuuuge. And he was, I felt every ounce of that enormous 7lb 2oz baby. 
The birth wasn't great because they were only happy if I was strapped on my back on the bed with a stomach monitor AND a scalp clip on the baby. Lying down was incredibly painful, I wanted to be standing/moving!
Funnily enough after a couple of hours of the weight of a full term baby and my fat belly on top compressing the veins at the back of the womb, the monitor started recording decelerations in the baby's heartbeat Funny that. I suddenly had every sodding midwife, doctor, janitor and tea lady in the hospital in my room shouting at me to push. He was out in a couple of pushes, no pain relief, and apart from a tear everything was fine, but I don't think I'll ever forgive the way they totally medicalised my birth DESPITE every test, growth scan etc coming back fine. (If there had been a problem I would be have been happily strapped to that monitor, trust me)
They barely spoke to me like a person, no encouragement or it was a shame. My second pregnancy and birth was better, perhaps because I didn't take as much shit, perhaps because they saw that my first pregnancy and birth was completely uneventful. I went 11 days over and they were "threatening" induction, but I refused because by my dates I was only 4 days over, it was them who had put me forward a week. They weren't happy about this at all but I'd had enough of them dictating how my births should go. I went into labour 11 days over naturally, contracting nicely until I got to hospital and they stopped because I was so scared of the hospital.
Anyway after a couple of hours of walking I got them going again and then they got me on the monitor again, stuck a really painful IV out of the side of my wrist "just in case" then tried twice to do an epidural. It didn't work but I didn't need it anyway, I was actually coping quite well although I doubted myself initially. I stopped them trying to put it in a third time because I could feel the baby crowning. Once again, a couple of pushes and she was out, a truly ginormous 7lb exactly. At least since I was sitting up for the epidurals I wasn't flat on my back again so there were no decelerations, although due to the odd position I did tear upwards, which was nice... They wouldn't take the painful IV out for nearly 2 days because they were determined something would go wrong at some point. I'm going for an active birth next time and they can kiss my arse.
I wrote all this for you to see that even if you're a heffalump like me there's no guarantee that anything will go wrong, so don't worry, and don't let them scare you. I have two beautiful healthy (slim!) children to show for it, thank god. I'm not saying nothing can or will ever go wrong but all you can do is try to eat healthily, maintain gentle exercise, do the tests, have intermittent monitoring and hope for the best! No need to scare the pants off new mums imho! 