On a late July day a few summers ago, my wife and I were wandering around the stunning campus of the Getty Museum in Los Angeles when my wife’s phone rang. After listening for a minute, she burst into tears.

Clueless, as is often the case with me, I immediately jumped to the worst possible conclusions until my wife managed to convey to me that nothing was wrong. Why, then, the tears? When the call concluded she explained that our younger daughter’s husband had just received the results of a test that verified that he was not a carrier for cystic fibrosis, and that now the baby-making could begin.

We were thrilled, but it reminded us of our own fraught history with this decision.

Shortly after the birth of our first daughter, my sister gave birth to her second daughter, Emily. Within hours of her birth, the doctors knew something was wrong, and they quickly suspected cystic fibrosis. My family knew nothing of this disease, but we all soon learned that it affected lung function and that it nearly always (at that time) resulted in an early death.

Emily herself complained little as she endured frequent hospitalizations and various therapies intended to help clear her lungs. She was an exceptionally articulate little girl who knew the words to the movie “Grease” by heart because it was one of the first VHS tapes her parents possessed.

My wife and I had assumed we would have another child in a couple of…