So finally we could put our cheque book away and let the NHS take the strain. It was a relief as apparently babies can cost a bit so we figured we might need to save.
Our consultant at Jessops is Mr Jokhi. He's really nice, if a little doom ladened. First scan with him he saw that there was a membrane between the twins - phew! That was a great relief. He then told us the next thing to worry about was Twin to Twin Tranfusion Syndrome - where the flow of blood from the placenta can be too much to one twin and too little to another. 'If you get to 24 weeks without that we can rule that out' he said. More waiting.
Bad news was that he checked the babies nucal folds (a sign of Downs) and one twin had a thicker than normal fold. As the other twin didn't he thought it might be that one wasn't growing right - structural issues.