A procedure used in conjunction with in-vitro fertilization to screen for specific genetic or chromosomal abnormalities before transferring the fertilized eggs into the mother. The technician removes one or two cells about three days after fertilization, then examines the chromosomes for obvious abnormalities such as trisomies (three chromosomes instead of the normal two) or aneuploidy (change in the number of chromosomes that can lead to a chromosomal disorder).
PGD is controversial. Some practitioners recommend the technique for couples experiencing recurrent miscarriages with the idea that pre-screening might reduce the incidence of miscarriages due to chromosomal abnormalities. The evidence is not yet conclusive on whether or not the technique is helpful to increase successful pregnancy rates.
