hi there
i was told I could do this from 11 weeks onwards. I have just booked it for the day I am exactly 12 weeks.. they should understand if you have to go a few days earlier and i think this is usually ok, after all it is your risk that you have to pay again for another one. I think worth it for the dad to see the little one!persevere! i think often the people you deal with forget just how exciting this is for you as they deal with it every day!