When a drug to prevent babies from being born too early won federal approval in February, many doctors, pregnant women and others cheered the step as a major advance against a heartbreaking tragedy.

Then they saw the price tag.

The list price for the drug, Makena, turned out to be a stunning $1,500 per dose. That’s for a drug that must be injected every week for about 20 weeks, meaning it will cost about $30,000 per at-risk pregnancy. If every eligible American woman were to get Makena, the nation’s bloated annual health-care tab would swell by more than $4 billion.

What really infuriates patients and doctors is that the same compound has been available for years at a fraction of the cost — about $10 or $20 a shot.

“It’s outrageous,” said Helain J. Landy, chairman of obstetrics and gynecology at Georgetown University Hospital. “Raising the cost of each injection from around $20 to $1,500 is ludicrous.”

Makena, a recently approved drug to prevent preterm births. (KV Pharmaceutical Co.)

The company that owns Makena, KV Pharmaceutical of St. Louis, says the price is reasonable, given that it is spending more than $200 million to develop the drug and conduct follow-up studies that the Food and Drug Administration demands, and because of the savings resulting from preventing preterm births. Through a subsidiary, Ther-Rx Corp., the company created a program to help women who can’t afford it.

“Ther-Rx is fundamentally committed to the community of women, children and families it serves and has been carefully listening to all stakeholders following the announcement of the list price for Makena,” the company said in an e-mail.

Critics are challenging that claim, noting that the main study used to demonstrate the drug’s effectiveness was a $5 million project conducted by the National Institutes of Health — paid by taxpayers.

“It’s not like this drug is something they invented,” said George Saade, president of the Society for Maternal-Fetal Medicine, which, along with the American Congress of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics, sent KV a letter protesting Makena’s price. “I think the company is taking advantage of their FDA approval and their monopoly to make money.”

In addition to making the drug unaffordable for some women, experts fret about the added costs for insurers that choose to pay for it, especially Medicaid programs already being slashed in states struggling with deficits.

“I’m worried about the patients not being able to afford the medication. I’m worried about our health-care system not being able to afford to pay this kind of price for a medication. And I’m worried about a process that enabled a drug that was readily available to go on to be become very expensive,” said Hal C. Lawrence III, vice president of practice activities at ACOG.

The case has put a spotlight on the March of Dimes, which has received about $1 million in donations from Ther-Rx and praised Makena when it was approved, only to later criticize the price.

“They were clearly holding back the price until after the FDA approval process,” said Alan R. Fleischman, March of Dimes’s medical director. “When we found out, we were as outraged as everyone else.”

More than 500,000 of the 4.2 million women who have babies each year give birth prematurely, and many of the babies don’t survive. Those who do are at increased risk for many health problems, including mental retardation, cerebral palsy and autism.

A form of progesterone known as 17P was used for years to reduce the risk of preterm birth, but it fell out of favor after the manufacturing company stopped making it. In 2003, the NIH study showed that 17P could cut the risk of preterm delivery if given in the first 16 to 24 weeks of pregnancy. That led to a resurgence in the use of 17P. Because no companies marketed the drug, women obtained it cheaply from “compounding” pharmacies, which produced individual batches for them.

Doctors and regulators had long worried about the purity and consistency of the drug and were pleased when KV won FDA’s imprimatur for a well-studied version, which the company is selling as Makena.

The approval of Makena gave the company seven years of exclusive rights, and KV immediately fired off letters to compounding pharmacies, warning that they could no longer sell their versions of drug.

“Continuing to compound this product after FDA approval of Makena renders the compounded product subject to FDA enforcement for violating certain provisions of the Federal Food, Drug and Cosmetic Act, as well as FDA guidance,” the letter says.

After word of KV’s actions began to spread, Internet sites for pregnant women became filled with angry commentary. Some created Facebook pages lambasting KV.

“I think it’s disgusting,” said Della Leahy, 34, of Fairfax, who is taking 17P to prevent her fourth pregnancy from ending prematurely. Leahy has two children but lost a son in 2008 who was born prematurely. “It just seems like the company is out for a huge gain of money. It’s very upsetting.”

Each insurance company and state Medicaid program must decide whether to cover the drug. But even women whose insurance will pay could face thousands in out-of-pocket costs to satisfy co-payments and deductibles.

FDA officials said that they had no idea how much the company planned to charge for the drug and were surprised by the cost but that the agency has no power over pricing.

In an interview with The Washington Post on Friday, an FDA official said that, if requested, the agency could approve a lower-priced generic version of the drug for another use that doctors could prescribe “off label.”

In addition, the official said the agency would not prevent compounding pharmacies from continuing to provide 17P unless patient safety is thought to be at risk.

“We have our hands full pursuing our enforcement priorities,” said the official, who spoke on the condition of anonymity because of the sensitive nature of the issue. “And it’s not illegal for a physician to write a prescription for a compounded drug or for a patient to take a compounded drug. We certainly are concerned about access of patients to medication.”

Several members of Congress have sent letters to KV complaining about the price and demanding justification and have asked the Centers for Medicare and Medicaid Services and Federal Trade Commission for investigations.

Outside experts said the FTC could sue KV if it concludes the company is illegally impairing competition.

“It threatens to extract significant competitive harm on extremely vulnerable pregnant women, and it threatens to significantly inflate health-care costs at a time when controlling health-care costs is a critical national priority,” said David Balto, a Washington antitrust lawyer who worked at the FTC.