As an Ashkenazi Jew planning to have a baby, I sure as heck wanted carrier screening for Tay-Sachs disease. But that disease is incurable and lethal. What about diseases that don’t severely limit lifespan and aren’t that disabling? During my pregnancy, I went on to have amniocentesis, which included testing for Down syndrome and – because of my family history — for a few genes associated with autism and mental retardation. But even as I was tested, I had no idea what I’d do if results came back positive.

Sometime soon, almost every expectant family may be faced with such life-and-death decisions. New tests are arriving that can detect Down syndrome by analyzing fetal DNA in the mother’s blood during the first trimester of pregnancy. …