Preimplantation genetic diagnosis

According to the Centers for Disease Control and Prevention, more than 45,000 babies are born each year with the aid of assisted reproductive technologies like in vitro fertilization. (IVF). Preimplantation genetic diagnosis has been used for more than a decade to screen embryos for hereditary diseases such as Down syndrome and other abnormalities. To do this, one cell from an eight-cell embryo is extracted and examined for chromosomal defects.

Theoretically, each of the eight cells should be identical. However, in up to 50% of embryos created by IVF, a type of mosaicism occurs in which some cells of the embryo have a different genetic complement from the other cells. Embryos that become mosaic after their cells divide twice typically stop progressing by the time they have accumulated eight cells. Too many of their cells have chromosomes that don't match and these mixed messages lead the embryo to stop developing, according to Larissa Kovalinskaia, an IVF researcher at the University of Florida. Thus, it is possible that the one cell removed for testing may indicate a normal embryo, while the embryo has some mosaicism and may not develop further or may develop a fetus with abnormalities.

UF researchers estimate less than 3 percent of healthy embryos are discarded as abnormal and only 1.5 percent are implanted with undetected genetic defects because of mosaicism.

But the small margin of error shouldn't stop couples from having preimplantation genetic diagnosis, said Jamie Grifo, a professor of obstetrics and gynecology at New York University. The testing can work miracles for women prone to miscarriages or who carry genetic diseases, he said. Screening embryos for genetic diseases offers couples the best chance for a healthy child.

(Much of the information presented here comes directly from a EurekAlert! article published today.)