Key Terms
Saviour Sibling - The term 'Saviour Sibling' usually (but not always) refers to a baby created using IVF, that was screened using PGD to act as a donor match for an existing sick child. To understand this, you need to understand the processes involved in IVF and PGD. PGS has been included below, because in creating a 'Saviour Sibling' you are screening embryos for two reasons:
- To check whether the embryo will develop the disorder that the existing sick child has (PGD)
- To check whether the embryo will develop into a child that is a donor match for the existing sick child (PGS)
When the new baby is born, it is common to use blood from the umbilical cord to treat the sick sibling. If this does not work, a bone marrow transplant, or some other tissue or even organ transplant, may be necessary at some later stage. The UK's first Saviour Sibling was actually born using PGS in 2003 (the disorder Jamie Whitaker had was not inherited, so there was no 'Diagnosis', just screening for a donor match) - and this could not happen in the UK as you can only screen if there is the chance of an inherited disorder.
IVF - In Vitro Fertilisation: where fertilisation happens outside the body. The man masturbates to produce sperm; the woman takes fertility drugs to produce several eggs, and a doctor harvests these, usually up to thirty eggs. They are mixed with the sperm in a petri dish, producing multiple embryos, each one genetically distinct. The embryos are grown, usually for 2-5 days, and the 'best' embryos (2 in the UK, as many as 5 in India) are chosen, based on number of cells, evenness of growth etc. and implanted. This has been happening since 1978. In 2011, success rates for IVF are about 1 in 3, although with multiple attempts, studies show that around two thirds of couples who try IVF eventually have a baby.
PGD - Pre-Implantation Genetic Diagnosis: screening IVF embryos to prevent inherited disorders. This procedure usually happens at about day 3, when the embryo is around 6-10 cells in size. Acid is used to get into the embryo, and an ultra-thin pipette sucks out one cell. The cell is screened, usually to identify whether the foetus might develop a genetic disorder (this is the only use for PGD in the UK). The first birth following PGD was in 1990, screening for Cystic Fibrosis. PGD can also be used to check if a new baby would be a donor match for an existing sick child (see Saviour Siblings)
PGS - Pre-Implantation Genetic Screening. In the US, embryos can be screened to identify gender, so that the parents can choose the sex of their child. This is usually called PGS, as there is no diagnosis involved (although in PGD there is technically no diagnosis either, as the embryo is not yet ill).
