Congratulations! It's a (You Choose) Boy/Girl
Every expectant parent prays for a healthy child, and some turn to science to try to ensure it. But now that it's possible to do genetic testing on tiny embryos, the question is: Which genes are good enough?
Preimplantation genetic diagnosis was invented in the 1980s to help patients using in vitro fertilization weed out embryos that carry deadly errors, like the gene for Tay-Sachs disease. But increasingly, PGD, which plucks one cell from a 3-day-old embryo when it is just a ball of six or eight cells, is being used for choices that are less clearly beneficial to the child. That includes having a baby that is an immunological match for an older, seriously ill child so that the baby's cord blood can be used for stem cell transplantation.
PGD is also used for sex selection, either to avoid diseases caused by mutations of the X chromosomemore common in boysor simply because the parents want a boy or a girl. According to a 2006 survey by the Genetics and Public Policy Center, 42 percent of clinics offering PGD have done it for nonmedical sex selection.
No guarantees. "It's amazing technology," says Robert Brzyski, an associate professor of obstetrics at the University of Texas Health Science Center at San Antonio, who leads the ethics committee of the American Society for Reproductive Medicine. The trouble is, he says, it's unknown whether the benefits of PGD outweigh the risk to the child. So far, the risks appear small. "But it's still possible," says Brzyski, "that it could be devastating for a small number of children," who might face a greater risk of disease in adulthood. PGD screening also doesn't guarantee a healthy embryo, as it can analyze just 9 of the 23 human chromosomes. That makes it problematic in screening embryos from women over age 35, which are more likely to have chromosomal abnormalities, as well as for women who have repeated miscarriages. There's no evidence that this ups the chance of having a baby. "The only measure that really matters is live birth," says Marc Fritz, chief of the division of reproductive endocrinology and infertility at the University of North Carolina-Chapel Hill.
ONLINE GENETICS RESOURCES:
- National Library of Medicine: Genetics Home Reference
- My Family Health Portrait: A Tool for Making a Family Medical History Report
- Genetic Alliance: A Genetic Disorder Advocacy Group
- GAO Report on Nutrigenetic Testing: Test From Four Web Sites That Mislead Consumers
This story appears in the January 8, 2007 print edition of U.S. News & World Report.