A doctor examined an Arizona woman who is in a vegetative state less than nine months before she gave birth, but did not find that she was pregnant, it has emerged.
Medical experts have said it is possible the 29-year-old woman displayed no outward signs which workers who cared for her every day would have noticed.
Police who are looking for her rapist said it appears none of the staff members at the Phoenix long-term care facility owned by Hacienda HealthCare knew about the pregnancy until the baby was born on December 29.
The notion has been met with some scepticism, but the patient, who is described in a medical report as having tubes to feed her and help her breathe, may not have had a swollen belly, according to a doctor.
Foetal medicine expert Dr C Kevin Huls said that while some factors remain unknown, such as how far along she was in her pregnancy, someone who is fed the same amount from a tube every day might not show any dramatic changes that would be noticed, especially by staff who do not work with pregnant patients.
The mother could actually lose weight in other places like her face or arms if a foetus is consuming nutrients, Dr Huls added.
"A good way to understand it is that really, the baby's going to continue to grow even at the expense of the mom's nutrition," Dr Huls said.
"So, her weight may not change because she's not taking in additional calories. There may be changes to her body that are going to go undetected in a chronic care condition or at a facility like this."
The revelation that an incapacitated woman was sexually assaulted inside a care facility has horrified advocates for people with disabilities and the community at large.
The provider's CEO resigned this week, and Arizona state officials said the centre has made safety changes.
A doctor examined the woman on April 16 and found "no change" in her health, writing that the examination was external only, according to Maricopa County superior court documents.
Her mother submitted the results of the physical examination as part of an annual report required of legal guardians under state law.
Phoenix police learned of the situation when they received a call on December 29 about a newborn in distress at the Hacienda HealthCare facility.
Officers launched a sex crime investigation when it was determined that the mother was in a vegetative state, Arizona police spokesman Tommy Thompson said.
He added: "She was not in a position to give consent to any of this."
The woman and her child are recovering at a local hospital.
Her family, who are members of the San Carlos Apache tribe in south-eastern Arizona, said in a statement through their lawyer that they will care for the baby boy.
Phoenix police, meanwhile, have not ruled out any suspects in the sexual assault. They are gathering DNA samples from the facility's male staff and have appealed to the public for any information.
It remains unclear to investigators if the woman was raped more than once.