BOSTON – A provocative study of newborn death rates finds strikingly few differences across the country and suggests there are far too many doctors and hospital units specializing in intensive care of premature or sickly babies.

Only newborns in areas with the very fewest specialists die at a higher rate than elsewhere. But once a certain threshold of care is reached, having even more doctors offers no extra advantage, the study says.

The researchers said this oversupply is not only a profound waste of medical resources, it may also be harmful, because it may subject babies to unnecessary tests and treatments.

The researchers “raise disturbing issues regarding the nation’s unquestioning acceptance that more is always better with respect to the supply of specialist physicians and hospital technology,” said Dr. Kevin Grumbach, a public health researcher at the University of California at San Francisco.

He wrote an editorial to accompany the findings, published in Thursday’s New England Journal of Medicine.

The researchers at Dartmouth Medical School in Hanover, N.H., knew of big disparities in the availability of specialized neonatal care from region to region. They wondered if places with more specialized doctors or beds relative to the number of births save more newborns.

The study found that for the most part they don’t. Only newborns in areas with very few such doctors, 2.7 for every 10,000 births, show a higher death rate – 7 percent higher than in better-equipped areas.

Other areas – with a supply of doctors ranging from 4.3 to 11.6 neonatologists per 10,000 births – all had about the same death rate. Even the most premature babies were found to die at roughly the same rate in these areas.

Moreover, the supply of neonatal intensive care hospital beds made no difference in death rates around the country.

“Enough may be enough,” said Dr. David Goodman, the pediatrician who led the study.

The neonatal care specialty has mushroomed since the 1970s, thanks to new technology and therapies, including ventilators designed for premature newborns and prenatal drugs that help fetuses’ lungs develop. Some babies born three months early, weighing barely more than a pound, now can be rescued.

However, the researchers suggested that social and economic factors have expanded the field beyond pure medical need. For doctors, the specialty can be gratifying, exciting and well-paying. For hospitals, it a lucrative and prestigious business.

The researchers said that because of the oversupply, some relatively healthy newborns may be subjected to unneeded tests and treatments that can produce harmful side effects.

“If I have a healthy full-term baby, I actually don’t want anyone messing around with that baby,” Grumbach said. “There’s a downside where we meddle too much.”

However, he said it would take deep changes in the medical system, with more government planning, to distribute neonatal doctors and beds much more uniformly.