For the first time in New Zealand a couple is to have an IVF baby chosen because its stem cells could cure an elder child born with a genetic illness.
The couple's doctor Mary Birdsall said they wanted to have a child using IVF so it could screened to make sure it didn't suffer the same illness as its sibling.
But they also wanted a second round of screening so they could choose an embryo which was a donor-match for their sick child. That way doctors could harvest stem cells from the umbilical cord blood and bone marrow of the baby to create a cure for its sibling.
Screening an embryo to see if is a donor-match has never happened before in New Zealand and needed special approval from an ethics committee.
"That required reports from a number of specialists, including geneticists, myself and counsellors. Then (the couple) had to wait for their funding to come through so this could go ahead. So it has been a fairly lengthy process," Dr Birdsall said.
She said part of the reason approval was given was that the couple wanted another child even if it wasn't a donor match.
And she is sceptical of people who think the case is the start of a slippery slope towards so-called 'designer babies'.
"This is a very unusual scenario. This couple has just opted to use science to make sure that they get a healthy child and - if it were going to be possible - also that this child would be a match for their existing sick child," Dr Birdsall said.