CGS-authored

"Mommy, where did I come from?"

Throughout history, parents have squirmed at that question because it involved sex. Now, many are squirming because it doesn't. For children born through in vitro fertilization -- 3 million and counting -- the answer involves injections, selections and lab dishes. The hard part is explaining the siblings we rejected: nearly half a million embryos frozen in U.S. clinics alone. In thousands of cases each year, the story now includes pre-implantation genetic diagnosis (PGD), a technique for weeding out flawed embryos.

What flaws are we screening for? That's the most uncomfortable question of all. Sometimes, the flaw is a horrible disease. But increasingly, it's a milder disease, the absence of useful tissue or just the wrong sex. If you think it's hard to explain where babies come from, try explaining where baby-making is going.

In its early days, PGD targeted fatal childhood diseases such as Tay-Sachs. But a new survey of U.S. fertility clinics, scheduled for release this week by the Genetics and Public Policy Center (GPPC), suggests that the line is moving. Among clinics...