So British couples wanting to choose the sex of their child must now go abroad, and the most common choice is the US, where sex selection is legal in every state. I realise this is not the correct thing to be doing now. The twins wriggle and clamber and tumble around the room. But he is puzzled by the British attitude. It is rare, he says, for people to sex select when they have no children already. They are lovely, lively girls. Ten years ago, the Trathens were in much the same position as the Gunns. They are, says Nicola, "completely different from the boys in every respect. Fifteen years ago, when I was pregnant with my first son, every mother had a scan at weeks of gestation — it was a standard part of obstetric practice, as it still is today there is also now an earlier scan at eight to 14 weeks.