The following article appears in the March/April 2007 issue of Technology Review.

A 38-year-old woman with fer­tility problems has three sons but wants a daughter to round out the family. She uses in vitro fertilization (IVF) to conceive and asks her doctors to transfer only female embryos; the male embryos are destroyed. Is this use of reproductive technology acceptable? What if a couple with a family history of diabetes wants to use IVF to select an embryo without a ­particular gene linked to diabetes risk? If afflicted family members largely have the disease under control, are the prospective parents justified in choosing in vitro fertilization so that they can bear a child with a lower chance of developing it at all?

Such questions are becoming more common as preimplantation genetic diagnosis (PGD)--testing performed after an egg is fertilized in vitro but before the resulting embryo is transferred to the womb--makes it possible for some prospective parents to select specific embryos before a pregnancy begins. Originally developed more than a decade ago to identify the rela­tively small number of embryos at high risk for serious or fatal genetic diseases, such as Tay-Sachs, the technology now encompasses genetic tests for a growing number of illnesses, including some that are not necessarily fatal. And these tests are available to more and more parents as the popularity of in vitro fertilization skyrockets; approximately 50,000 babies are born through IVF in the United States every year.