The disturbing case of an Arizona woman who gave birth despite being in a vegetative state for more than a decade is not the first of its kind, experts told NBC News.

The woman, 29, delivered in December while receiving long-term care at Hacienda HealthCare in Phoenix after a near-drowning incident. Authorities do not know who impregnated her and have opened a sexual assault investigation in search of her rapist.

The case echoes one from 1995, when a comatose 29-year-old woman was raped by a nurse's aide at her nursing home near Rochester, New York. Staff discovered she was pregnant early on, a key difference between her and the Arizona woman.

Jeffrey Spike, an affiliate faculty member at the University of Virginia School of Medicine Center for Biomedical Ethics and Humanities, served as an ethics consultant for the hospital treating the New York woman and spoke with her parents about whether they wanted to terminate the pregnancy. They decided against it, and the woman gave birth to a premature but healthy boy in March 1996, who was raised by his maternal grandmother.

In patients in vegetative states, Spike said, "cognitively, all the human qualities are gone, but biologically, everything is pretty normal," making it possible for pregnancy to happen.

"Whatever caused their daughter to be in a vegetative state was such a horrible tragedy already, and then to discover that she was raped and then to have to make this very difficult huge decision, was really very tough," Spike said.

Other women have been in vegetative states or brain dead while pregnant, but their brain function became compromised during pregnancy — not beforehand, said Dr. Deborah Feldman, the director of maternal-fetal medicine for Hartford Health Care in Connecticut.

In 2000, Feldman co-authored a paper on maternal brain injury which reviewed 11 cases of irreversible brain injury in pregnant women and found that 10 out of their 11 babies had survived. The cases included mothers who were brain-dead and in persistent vegetative states.

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The difference between a vegetative state and 'brain-dead'

Cases of brain-dead women who are artificially kept alive during pregnancy have made headlines, including Marlise Munoz, a Texas woman who suffered a pulmonary embolism while pregnant. Munoz was ultimately disconnected from life support after a legal battle and the fetus, who the family said showed abnormalities on ultrasound, died too.

Dr. Rezvan Ahmadi, a senior attending neurosurgeon at the University Hospital of Heidelberg in Germany, has researched brain-dead pregnant mothers and said patients in vegetative states are treated very differently.

"Brain death in Germany is defined as the death of the human being, and every guideline is regarding saving the life of the baby and also to save organs for organ transplantation," she said. "Vegetative persons are alive, so we cannot do anything to end their lives, therefore there is no question that everything has to be done for saving the life of a baby and saving the life of a mother."

In a vegetative state, patients can breathe and regulate their heartbeat on their own, but receive nutrition and hydration and show no signs of awareness.

"You will see eye-opening happen ... but there isn't any ability of the other parts of the brain in terms of understanding language, expressions of people's faces, things of that nature," said Dr. Gregory O’Shanick, medical director emeritus of the Brain Injury Association of America. "There's also not any kind of purposeful behavior that they're exhibiting, so you may see random movements, they may make a sound, and they may move once or twice, but it's not reproducible or consistent."

"There is no doubt in my mind personally and medically that this was an assault."

O'Shanick said there would be "no way" that someone in a vegetative state could give consent to a sexual encounter and said that with the Arizona woman, "there is no doubt in my mind personally and medically that this was an assault."

Pregnancy in patients with brain injury

The brain injury that caused the vegetative state, O'Shanick added, would not likely contribute to any physical challenges in a pregnancy.

"Unless there was some other type of physical injury, a fracture or some other type of spinal cord injury, then everything else would presumably be intact," he said. "The key issue is was she still having her period, and presumably the answer is yes."

And a lack of prenatal care, while important, may also not have affected the baby, said Feldman, the maternal-fetal director. Potential problems with a patient in a vegetative state would mostly be centered around their lack of movement and would include fetal growth restriction, poor placental function, elevated blood pressure, or gestational diabetes, among other issues, she said.

"It's hard to know for sure, but if there are no significant birth defects and if the baby was normally grown, there's every expectation that the baby will thrive and be normal," she said.

How could no one have known?

All the experts said that while it was surprising that Hacienda staff apparently didn't realize the patient was pregnant, it could have gone unnoticed depending on the size of the woman's midsection.

A doctor who examined her in April, eight months before she gave birth, noted nothing about a pregnancy, the Associated Press reported on Thursday, although it may have been too early.

"I would expect someone who was bathing her would notice, but I don't know what the level of care was," Feldman said. "You would expect her belly to be growing over nine months, but sometimes things like that show up differently on different patients."

If she felt anything different in her body, it would have been impossible to communicate those changes to her caretakers, said O’Shanick of the Brain Injury Association of America.

"Might they have noticed anything in other secondary changes, in terms of the size of her breasts and other things? It depends on the staff and what they were tracking, but this isn't something you generally track," he said. "You don't think in those terms. I can guarantee you that from now on, people are going to be thinking in those terms."