Kim and Aaron have chosen James to be their donor. He’s exactly what they’re looking for - the physical features, the profession, and dozens of photographs of donor-conceived children on his Facebook profile page that prove he can get women pregnant.

Even better, the couple don’t even have to meet him in person to conceive - he will ship his sperm to them via the post, and they can inseminate in the comfort of their home.

But as the months pass without success, despite repeated attempts, they are becoming disheartened. They come to meet him for an in-person donation, which raises the possibility that Kim could receive his sperm through “natural” insemination, or sex - a red line for Aaron, but not for her.

Dr Keenan Omurtag, a fertility specialist, guides us through what we know - and importantly, what we don’t know - about conception.

Presenter: Aleks Krotoski