Just doing some quick googling... and it looks like you have about the same chances (statistically) of having a placenta previa as you do of having a uterine rupture. The chances of an omphlocele are much, much lower.
I don't just understand the need to predict every single RARE problem that *might* happen to you or your baby. Yes, maybe some problems can be diagnosed or fixed early, but you're also setting yourself up for other issues by having the ultrasound to diagnose these things. What if they *think* they see a potential problem and you get risked out of a homebirth, only to find out that nothing was wrong? What if that diagnosis leads to a cascade of interventions that actually cause MORE harm to you and/or your baby? And what about the stress of worrying about potential problems (that may or may not resolve themselves) for the rest of your pregnancy?
I know that doesn't work for everyone, but for me I'm really trying to just trust in my body to do what it should, and in my intuition to tell me if something isn't right and I need to transfer to a hospital. I trust my midwife to know what to do if there is a problem.