(CNN) News of a woman in a vegetative state for more than a decade giving birth to a boy on December 29 has stirred emotions nationwide.

The rare medical event raises many questions, including: How can a woman who is unconscious give birth?

"It is very rare," said Dr. Deborah Feldman, who has heard about "maybe two or three cases" in the past two decades. Feldman, director for maternal fetal medicine at Hartford HealthCare Medical Group, treated a woman 20 years ago who had a stroke that rendered her brain-dead during her second trimester and who went on to have the baby. Feldman has read about, but has no direct knowledge of, the Arizona case.

The new case "speaks to the fact that the patient actually had largely normally functioning organs," Feldman said. "I can say that, biologically, her body actually was functioning very well in order to grow a full-term baby." Because she is the victim of sexual abuse, CNN is not reporting the name of the patient, who was in long-term care at a Phoenix medical facility.

A person in a coma is unconscious, though breathing independently, for a prolonged period of time. If a coma continues, it is considered a "persistent vegetative state ." By contrast, a brain-dead patient is unconscious, has lost the capacity to breathe and requires mechanical respiration.

Though it is unusual that no one noticed the Arizona patient's pregnancy, many healthy women deliver babies with no prenatal care. "Most of the time, those babies are healthy and robust," Feldman said. "Nature takes care of itself."

She believes the same will be true of the child in this case. "In a persistent vegetative state, your organs still work, and your fertility is still there," she said.

The risks in such cases would be poor fetal growth as well as all the usual risks of pregnancy found in healthy women, including diabetes and hypertension.

"Patients who are not moving don't really have any caloric expenditure, but they're also not eating," Feldman said. "My guess is that she probably had a feeding tube. That really helps with the nutritional support, and babies tend to grow well even with just that." Unlike IV fluids, a feeding tube is surgically placed in the stomach instead of a vein and provides formula for a patient.

When a patient is unconscious and unable to push, delivery is "very difficult," Feldman said. "In most cases, we rely on medication to strengthen the contractions -- so that would be oxytocin administered in an IV. That allows the contractions to be strong enough so the patient doesn't have to do anything." During the delivery, doctors would use forceps or a vacuum to assist.

"Always, a c-section will be the easiest way to deliver the baby, but obviously that's riskier for the mom because it is a surgical operation," Feldman said. "The recovery would be essentially the same as for a normal patient, with probably slightly increased risk of infection."

"It's hard to know" whether the woman knew that she was pregnant (or delivering a baby) or whether she experienced pain, Feldman said, without knowing the specifics of the woman's brain injury.

"I can tell you that to go through labor and deliver a baby with absolutely no analgesic is difficult, but I can't speculate as to what this patient felt, if she felt any pain, if she knew it was happening," Feldman said. "It's so sad she had to endure that. It's awful."

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"I feel like every five to 10 years, this comes up somewhere in the country, and usually, I get an email or a call because someone sees the paper that I wrote," said Feldman, who researched about 10 additional cases beyond her own patient.

Thaddeus Mason Pope , director of the Health Law Institute at the Mitchell Hamline School of Law in Minnesota, wrote in an email that the case illustrates the issue of patient safety in long-term care.

"Obviously, the biggest issue is the criminal battery that caused her impregnation," said Pope, who has no direct knowledge of the Arizona woman's case, as this was clearly not consensual sex.