Congratulations!
Please try not to worry too much. Be honest with your midwife about how you're feeling about this when you have your booking appointment.
As long as you're aware that there are some things they will have to mention/discuss/warn you about due to your BMI and are open to accepting that, and knowing they're doing it for the health of you and your baby rather than some personal attack, you'll be grand. It's not ideal to diet in pregnancy but you can follow Slimming World whilst pregnant as it's more about eating a healthy balanced diet rather than calorie restriction.
I was a similar size and weight when I fell pregnant. It wasn't ideal but I was told that if I wanted children to do it sooner rather than later (due to a totally unrelated condition). My plan was to get my coil out, let my cycles settle down a bit, lose some weight and maybe fall pregnant after 6-12 months or so. Nope, it took a week!
Fortunately, I had a totally normal pregnancy. I worked up until 37 weeks (was being induced at 38) and was at the gym doing a spinning class the evening before I was induced! I took a higher dose of folic acid, I took aspirin and had a test for gestational diabetes but that was fine. I too was worried about scans (and I had a lot due for reasons unrelated to my BMI!), but every one of them was fine (I had 13 in total, both NHS and private). They were all perfectly clear as well.
I'm not sure my weight was ever said out loud. Other than my booking appointment with my midwife I was only ever weighed at the hospital where I'd be taken off to have weight, blood pressure, urine sample etc. and my husband would just stay in the waiting room as the HCAs would do it before the actual appointment.
Your relationship with your partner is going to go to a whole new level. In about 7-8 months he's going to see you bring his child into the world. He's going to be your support and your advocate when you're at your most vulnerable whilst you do so. He's not going to be worrying about what the number on the scales says.
Enjoy the journey you're about to go on, don't let your weight worries take that away from you