I can't see the problem tbh. It's up to the propesctive parents and the guidance of the consultant to decide. Who are we to tell someone else who desperately wants, say, a baby girl 'tough titties, you'll get what you're given like it or lump it?'
I personally would love a baby, and wouldnt give a monkies about the sex of it. But that's me - and my wants and needs do not suit everyone.