The major barrier to Ms. Little’s simply choosing her children’s height is ease. To her, P.G.D. to select for dwarfism is too invasive; however, if having dwarf children were simply a matter of trying to conceive at a certain time of the month or taking a pill, she said, “I would do that.”

Barbara Spiegel, a homemaker in Maine who has dwarfism, had a first pregnancy that ended in miscarriage. She underwent genetic testing during her second pregnancy, and because of a laboratory mix-up involving petri dishes, was told that her child would grow to normal height. She would have loved the child, she said, but in an interview, she recalled thinking, “What is life going to be like for her, when her parents are different than she is?”

She worried that the child would be teased excessively. Ms. Spiegel’s best friend, who has average height, has a daughter with dwarfism, and the child sometimes comes to Ms. Spiegel for support; maybe an average-size child would also go to others for motherly advice. For a brief time, Ms. Spiegel grieved because she felt a dwarf baby would have been “just precious.” But after a week, the mix-up was detected and she got her wish.

Genetic testing for dwarfism has an extra ethical wrinkle. When both parents are dwarves, their embryos have a 25 percent chance of normal height, a 50 percent chance of dwarfism, and a 25 percent chance of what is called a double dominant mutation, which is usually fatal soon after birth. Because many dwarf mothers worry that their fetuses might have the fatal mutation, those who conceive without assistive technology, like Ms. Little and Ms. Spiegel, often undergo amniocentesis or chorionic villus sampling to detect double dominant mutations. Many consider abortion if the test is positive — but many would carry either a dwarf or an average-height child to term.

Preimplantation genetic diagnosis can identify embryos with double dominant mutations, so they can be discarded before implantation, while preserving embryos destined for either dwarfism or average height. In dwarves, then, P.G.D. could help avoid many doomed pregnancies if double dominants were never implanted. But then a choice would have to be made, since the genes are known. And many dwarves might select embryos for dwarves — although others might choose those for average-size children.

Dr. Stéphane Viville, who first reported P.G.D. for dwarfism in 2003 in France, used it to eliminate embryos with dwarfism among couples where one member was a dwarf and the partner had average height. Interestingly, if confronted with a situation where both parents were dwarves, Dr. Viville says that he most likely would implant only an embryo destined for normal height — and forbid not only double dominants but also dwarf embryos.

I think Dr. Viville fears that P.G.D. could be used willy-nilly to make genetic freaks. Yet the same fears pervaded the issue of in vitro fertilization decades ago. The small number of P.G.D. centers selecting for mutations doesn’t bother me greatly. After all, even natural reproduction is an error-prone process, since almost 1 percent of all pregnancies are complicated by birth defects — often by more disabling conditions than dwarfism or deafness.