“I’m pregnant,” my patient’s wife told me, her face a tapestry of conflicting emotions. My patient was watching her, too, trying to figure out if he should echo her happiness, or her grief.

“I’d like to offer congratulations, but I can’t tell if that’s what you want,” I said, trying to feel her out. She had been holding her breath for what seemed like minutes, and finally exhaled before answering.

“I don’t know if I want to go through with the pregnancy.”

My patient flinched a bit, but didn’t say anything. Both he and his wife were in their 30s, and he had been given a diagnosis of chronic myeloid leukemia a year earlier.

C.M.L. is one of our great success stories in cancer therapies. In 2001 the drug imatinib was approved by the Food and Drug Administration to treat the disease, and was so effective that almost immediately the number of C.M.L. patients who required bone marrow transplantation plummeted. Over 90 percent of patients achieve some sort of remission, which lasts for years in the majority. Since then, four other pills have been approved by the F.D.A. for C.M.L., each at least as effective, if not more so, than the original.

My patient wasn’t so lucky. His blood counts dropped to dangerously low levels with each medication we tried, none of which brought him close to a remission, and it appeared likely that he would need a bone-marrow transplant in the next few months, a procedure that carried with it risks of serious health problems, and even death.

“What’s going through your mind?” I asked her.

This time her husband responded. “I was taking the chemotherapy when she got pregnant. We’re worried about birth defects.”

This was terrain I had traversed before. Data about pregnant women exposed to chemotherapy for treatment of cancer, summarized in a National Toxicology Program report, show an apparent rate of major congenital malformations of 14 percent following first trimester exposure, and 3 percent thereafter. The qualifier apparent is used because these are only estimates, as information about birth defects is not rigorously reported. For men on chemotherapy at the time of conception, the data are even sparser.

As a result, we adjust recommendations about whether or not to continue with a pregnancy based on the timing of chemotherapy relative to the pregnancy, whether it is the man or woman who is exposed, and on the known likelihood that the chemotherapy will cause birth defects or fetal mortality. For patients who are pregnant in their first trimester with a new diagnosis of acute leukemia — a cancer requiring high-dose chemotherapy that is almost certain to induce death of the fetus — I have recommended termination, as a blighted pregnancy would endanger the life of the immunocompromised mother.

In this case, though, I thought the risk of birth defects were low, and explained this to my patient and his wife.

He smiled and looked over to his wife, as if expecting her to join in his relief. But she still looked torn, staring straight ahead, somewhere into the space between him and me.

“But he’s going to have a transplant. What happens if I have this baby and he’s not here to be its father?” she asked, now looking directly at me. Tears had started to wind down her cheeks.

I reached for a box of tissues to hand to her, half expecting her husband to say something encouraging about his prospects, to alleviate her fears. But he sat quietly, rubbing her back, staring into that same space she had occupied a few moments earlier. Perhaps he was struck silent by her honesty; or perhaps, by the reality of his condition.

“Hopefully the transplant will go smoothly, he’ll be cured of his leukemia, and we’ll all look back at this conversation and wonder why we even had it,” I told her. His focus shifted back to us.

“But you both know,” I continued, “there are no guarantees. On the one hand, it will be hard to care for a baby and for him as he goes through the transplant. It may be even harder if he doesn’t survive.” They nodded in agreement.

“On the other hand, if the worst happens, and he dies, you’ll still have a part of him that will live on.”

They sat in silence, my patient and his wife, each thinking about their possible futures: one with him present as a father, and one without.

This wasn’t my decision to make, or one in which I could provide any more informed advice. I sensed they wanted time to be alone, and said goodbye as I got up to leave.

My clinic rooms, clean and nondescript as they are, sometimes provide a safe house for laying bare the difficult thoughts, the wrenching decisions, that tug on my patients. I couldn’t guide this couple on what to do about the pregnancy, but they weren’t really asking me to.

They just wanted to be heard. By me, but more important, by each other.