WASHINGTON - Federal health officials say the parents of premature babies enrolled in a study of oxygen treatment several years ago weren't properly informed of the risks: a kind of blindness or death.

Oxygen has been a mainstay of treatment for very premature babies. But too much has long been known to cause a kind of blindness called retinopathy of prematurity, and too little can increase risk of death. The study in question enrolled 1,300 babies at 23 hospitals between 2005 and 2009, to hunt the best dose somewhere in between.

Standard practice at that time was to use a particular range of oxygen, and researchers in the study, funded by the National Institutes of Health, randomly assigned babies to receive either the low end or the high end of that range.

The study's stated intent was to determine how much oxygen minimized the chances of blindness without increasing the risks of other problems including death or brain damage. The problem: The informed consent document that parents had to sign to enroll didn't spell out those risks, according to the government's Office for Human Research Protections.

In a letter to the University of Alabama at Birmingham, which led the study, the government agency concluded the research had violated regulations requiring that patients be fully informed of the risks of a clinical trial. The March 7 letter, which was publicized Wednesday by the consumer advocacy group Public Citizen, asked the university to take steps to ensure consent forms in future studies outline all the risks.

In a statement, university's vice president for research Richard Marchase said although slightly more babies who received lower-dose oxygen in the study died, those death rates still were lower than was usual for premature babies getting standard care at the time.

But, "we will ensure that any future consent form clearly delineates risks to all arms of a study as completely as possible, including studies in which all arms are operating within the accepted standard of clinical care," Marchase wrote.

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