The marrow will come from her baby sister, Marissa. Their parents say they conceived Marissa to provide bone marrow to save Anissa's life.
Doctors and ethicists say this is the first time a family has publicly admitted conceiving a child to serve as an organ donor. But many others have done so privately, conceiving babies to provide bone marrow for siblings and relatives or even, in one case, a kidney.
In the case of the Ayalas, their decision to conceive a child as an organ donor was declared in public for all interested parties to examine.
Ethicists and doctors are asking whether conceiving a child as a source of donated organs violates the principle that individuals should be brought into the world and cherished for their own sake and no other motive.
Others argue that the children who are conceived to donate organs are deeply loved and that it is unfair to point fingers at parents who have a child to save another person's life. From the point of view of the child, it is certainly better to have been conceived to donate than to have never been conceived at all.
It may even be justifiable to abort a fetus of the wrong tissue type some experts say, but others say they cannot condone this.
At first, said Dr. Steven Forman, the City of Hope transplant specialist who is caring for Anissa, transplant experts were saying, "What's the big deal? This happens all the time."
But as the case gained attention, Dr. Forman said, he began to ask himself why he found it acceptable to conceive a child to be a donor and why, if it were so acceptable, doctors and parents had kept quiet about it until now.
In conceiving Marissa, the Ayalas were seeking to escape from a desperate dilemma. Their daughter Anissa has chronic myelogenic leukemia, a disease that kills 80 percent to 90 percent of patients within five years of diagnosis.
Her only hope is a bone marrow transplant, Dr. Forman said, and even then her survival is far from assured. Even with a marrow transplant, 20 percent to 25 percent of patients die, usually of infections, adverse reactions or a return of the leukemia.
When Anissa was diagnosed four years ago, she and her family began searching for someone whose tissue type was compatible with hers and who would be willing to donate marrow.
There is little risk to the marrow donor, other than discomfort. The donor is anesthetized while doctors poke long needles into the hip bones and withdraw precious tubes of the dark red marrow.
The patient, meanwhile, has undergone four days of intensive, whole body irradiation followed by high doses of chemotherapy so as to destroy completely every cell of her or his own cancerous marrow. As soon as the donor's marrow is drawn, it is dripped into the patient's bloodstream, where it finds its way inside the bones and grows there.
But the Ayalas could not find a compatible donor. Neither parent had the right tissue type, nor did their son, Airon, who is 20. A nationwide search for an unrelated donor found none.
Last February, the Ayalas, who live in Walnut, Calif., announced their decision to conceive a baby as the best hope of finding compatible marrow for Anissa. Abe Ayala, the father, had to have a vasectomy reversed. The mother, Mary Ayala, was 42 when she conceived.
Dr. Rudolph Brutoco of Covina, Calif., the baby's pediatrician, said Mrs. Ayala had amniocentesis when she was 6 months pregnant and had the fetus' tissues typed.
The reason, Dr. Brutoco said, was not to have an abortion -- it was too late by then -- but to learn if the baby could be a donor. If the fetal tissues matched Anissa's, doctors would save the baby's umbilical cord blood to give along with her marrow when Anissa had her transplant. Marissa was born April 3, 1990.
Dr. Forman said he and the other doctors on the transplant team took "an educated guess," that the best time to attempt the transplant would be when Marissa was 14 months old, balancing Anissa's limited time when she would be healthy enough to have a marrow transplant with their desire to allow Marissa time to grow and develop.
Anissa was admitted to the hospital May 22 and her marrow has now been totally destroyed -- she cannot make any red or white blood cells on her own and will die without her sister's marrow.
When the donor is a baby, the parents give permission. When child donors are old enough to be included in the discussions, the doctors describe the donation process to them and ask them if they want to be donors, Dr. Forman said. Most readily agree, he added.
Decisions like the Ayalas' are apparently not as uncommon as might be expected. Last fall, Dr. Arthur Caplan and Dr. Warren Kearney of the Center for Bioethics at the University of Minnesota surveyed 15 of the nation's 27 bone marrow transplant centers, including the 10 largest ones, asking doctors and nurses whether they knew of similar cases and, if so, what had become of them.
"We found at least 40 children had been conceived for the purpose of bone marrow donation in the past five years," Dr. Caplan said. Most were conceived to help an older brother or sister, some for the aid of parent or cousin.
Transplant specialists said Dr. Caplan and Dr. Kearney might have uncovered just a fraction of the cases. Parents usually do not discuss their decision to have another baby with their transplant doctors, said Dr. Patrick Beatty, a bone marrow transplant specialist at the University of Utah.
In his survey, Dr. Caplan said, he learned of one couple who conceived three children in an unsuccessful attempt to have a donor.
In another family, a woman was divorced and remarried when a child from her first marriage needed a bone marrow transplant. So she was artificially inseminated with semen from her former husband to conceive a baby to save the child.
Dr. Norman Fost, a pediatrician and ethicist at the University of Wisconsin School of Medicine, said he has been involved with several families who had babies because they needed a donor. "It's not rare," he said.
In one case, a couple conceived a child hoping for a bone marrow donor. They sought prenatal testing with the intention of aborting the fetus if it were not a match, but their obstetrician refused.
Dr. Robert Levine, an ethicist at Yale University's School of Medicine, said he too was troubled by the idea of having babies to be donors and aborting fetuses that were not the right tissue type.
"The ideals of our society are that we are to treat each person as an end and never merely as a means," he said. "It seems to me that when a primary motive for conceiving a child is to produce tissue or an organ, we are getting very close to seeing this new being as a means to another end. This is what raises an ethical impropriety."