I'm not sure but it sounds like they have some kind of policy about how much the nursing staff can lift if needed, in and out of the bath?

I wasn't weighed either during pg but I didn't have the option of a water birth. It will really suck if you miss out because of a stupid number. Muscle weighs more than fat, as you no doubt know which to me means that you are more likely to be able to assist in getting yourself in and out of the bath (having the strength itms?) but I don't really know.