Genetic testing of embryos has been around for more than a decade, but its use has soared in recent years as methods have improved and more disease-causing genes have been discovered. The in vitro fertilization and testing are expensive — typically about $20,000 — but they make it possible for couples to ensure that their children will not inherit a faulty gene and to avoid the difficult choice of whether to abort a pregnancy if testing of a fetus detects a genetic problem.