Either increase BMI limit or change to fat and mascle mass limits because apparently muscle is denser and so weights more than fat, therefore if you are muscular, the muscle weight means you might remain over the BMI limit that fertility clinics put in place.

It's fair enough if the NHS keep the rule for their NHS funded treatment but private clinics should not have these rules. BMI doesn't always equal fat and plenty of people have high BMI and have children. Why should the right be taken away to have a family just because you can't conceive naturally? If you're paying towards treatment you should be able to at least sign a disclaimer to say you want to go ahead even with adviced high BMI. 

Everyone that is dedicated to being the best parent they can be deserves the chance have a family!