An ultrasound examination of a woman in the first three months of pregnancy costs about eight times as much at the Martha’s Vineyard Hospital as at nearby hospitals on the mainland.

Figures collated by the state on insurance payments for medical procedures show the Vineyard hospital to be vastly more expensive for outpatient services than the median across the state. In most cases the cost here is double, or more.

An ultrasound during the first trimester is $800 here, according to numbers from the state Division of Health Care Policy and Finance, part of the executive office of Health and Human Services. At the nearby Falmouth, St. Luke’s and Tobey Hospitals, the same procedure costs $100.

And the Vineyard hospital costs are not only vastly out of line with other hospitals in this region. A comparison of prices at 12 Boston area hospitals done recently by The Boston Globe, found even the most expensive of them, Massachusetts General (the parent hospital for the Vineyard hospital) charged less than a third as much, $263, for a first trimester ultrasound.

The state average is $150.

An ultrasound after the first trimester also costs $800 here, compared with $225 at Falmouth, St. Lukes and Tobey, and the state average.

And while the cost of ultrasounds is the number most out of line with providers elsewhere, there were many other procedures for which the Island hospital charged multiples of other institutions.

In five of six categories of outpatient procedures, the Island was among the most expensive in the state.

The median cost of a chest X-ray, for example, is $290 at the Martha’s Vineyard Hospital, more than three times the state median of $90. Falmouth’s cost is twice the average, while St. Luke’s and Tobey are just above the median.

The fee for an MRI of the lower back is $1,450, compared with $775 for the state and $650 at St. Luke’s and Tobey. For this procedure Falmouth charges even more than the Vineyard hospital, at $1,675. An MRI of the knee or ankle is $1,250, compared with a median $750 for the state, $600 at St. Lukes and Tobey, and $1,800 at Falmouth.

All categories of CT scan cost more than twice the state average here. A CT of the chest, for instance, is $1,175, compared with $525 for the state as a whole and $500 St. Lukes and Tobey.

Again by way of broader comparison, the survey of the dozen Boston hospitals showed even the most expensive of them was more than $300 cheaper than the Vineyard for this procedure. The most expensive Boston hospital is Mass General — again — and another affiliate, Brigham and Women’s.

For an echocardiograph, Martha’s Vineyard Hospital charges $550, compared with the state median of $350.

Indeed, the only procedure for which the Island hospital is not more expensive than 85 per cent of Massachusetts hospitals is a mammogram. That cost of $100 is in line with the state median.

It should be noted the numbers are collated by the state from a variety of sources and not all are recent. However, a spokesman for the Division of Health Policy and Finance said they are the most up to date available.

It should also be noted that the fees cited represent the cost to private insurers, not individual patients. However, medical sources say it is reasonable to assume in some cases that the high costs at the hospital are passed on to consumers, at least in part.

There is some anecdotal evidence of this. In one case, the insurer of a woman requiring two X-rays, to her neck and back, was billed $1,600 by the Vineyard hospital. Her insurer paid only $1,000, leaving her to pick up the other $600.

While negotiating with the hospital over the charge, she contacted another provider, who told her they would have charged her just $350, self-paid, for the same X-rays.

So, why does the hospital charge so much for these procedures?

When asked why an ultrasound should cost eight times as much here as at Falmouth, Martha’s Vineyard Hospital chief executive officer Tim Walsh said he could not speak to an individual charge.

“But I can tell you our charges would tend to be higher because our costs are higher,” Mr. Walsh said.

He said the Medicare wage index shows the Cape and Islands have the highest wage costs in the state.

“It’s 30 per cent higher than the average,” Mr. Walsh said. He continued:

“We have what turns out to be a pretty expensive model. We spend a lot on housing because we have to bring people over,” he said

There are also diseconomies of scale for a small hospital operating in a place where the population fluctuates wildly according to the season. The hospital must provide a wide range of services, but it is not necessarily fully utilized.

“The only time we’re really competitive in terms of volume is in the summer, when we can’t keep up. The rest of the year there tends to be a lot of stand-by cost,” Mr. Walsh said.

He also agreed that the high cost of some procedures can serve to cross-subsidize other loss-making areas.

“What you’re saying, in general is true. You have to when you have others paying less than cost; cross-subsidization happens,” he said. He added:

“We’re expensive because we’re an Island, and we’re a small hospital and it’s hard to make the model work.”

Medicare has recognized this by allowing the Island hospital critical access designation, which brings with it higher Medicare reimbursement.

“The reason Medicare did that is that we can’t live on the averaging system they have [for determining payments]. It just doesn’t work for us,” Mr. Walsh said.

And there may be other reasons why some procedures are more costly here. For example, the hospital only got a permanently-installed MRI machine in February. For years previously a mobile unit traveled back and forth on the ferry.

Mr. Walsh linked the hospital’s circumstances to the wider problems with the American health care system.

“There’s a piece of this that has to look at isolated hospitals and what that means to the cost structure,” he said, noting one of the suggested national reforms — computerized medical records — is already being implemented here, as part of the hospital’s affiliation with Mass General.

“We’re right now installing electronic medical records in our physician offices. That will mean less duplication of things.

“Right now, if you get an X-ray done here and you go up to Boston, that X-ray is available up there. That will be true of all services, once we get fully implemented.”

Doctors would also get advice through the system on how to handle particular cases: “to make sure that when you order a test, it’s the right test for the diagnosis you’re working on,” Mr. Walsh said.

“It will take a few years to get there, but I really think it’s going to help. It needs to,” he concluded.