Don't know about 3D or 4D but I expect it will just be 3D as I think 4D scanners are few and far between and more like a fetal portrait sitting, ie: not used for medical purposes but just if you want to see what the baby looks like...I think??? I have seen them advertised in pg mags.
Do Mercy do pg aqua classes at the hospital?? Would you recommend it and is it expensive or claimable thru insurance?