Preimplantation genetic diagnosis is a new method of prenatal diagnosis that is developing from a union of in vitro fertilization technology and molecular biology. Briefly stated, PGD involves the creation of several embryos in vitro from the eggs and sperm of an interested couple. The embryos are permitted to develop to a 6-to-10-cell stage, at which point one of the embryonic cells is removed from each embryo and the cellular DNA is analyzed for chromosomal abnormalities or genetic mutations. An embryo (...) or several embryos found to be free of genetic abnormalities are subsequently transferred to the woman's uterus for gestation. Embryos found to carry a genetic abnormality are discarded or frozen. Extra normal embryos may be frozen for future transfer or donation to another couple. (shrink)