Successful preimplantation genetic diagnosis to avoid creating a child affected by a genetically-based disorder was reported in 1989. Since then PGD has been used to biopsy and analyze embryos created through in viuo fertilization to avoid transferring to the mother’s uterus an embryo affected by a mutation or chromosomal abnormality associated with serious illness. PGD to avoid serious and early-onset illness in the child-to-be is widely accepted. PGD prevents gestation of an affected embryo and reduces the chance that the parents (...) will be faced with a difficult decision of whether to terminate the pregnancy. More controversial have been PGD to select the sex of the child-to-be for “family balancing”, PGD for mere susceptibility to disease and for late-onset disorders such as Alzheimer diseas, and most controversially, PGD to create a donor child who is Human Leukocyte Antigen (HLA-matched with a preexisting sibling in need of stem cell transplant. (shrink)