It was Labor Day weekend 2021 when Sara Walsh, who was 24 weeks pregnant with twins, began to experience severe lower-back pain.

On Wednesday, a few days later, a maternal-fetal specialist near her home in Winter Haven, Florida, diagnosed Walsh with twin-to-twin transfusion syndrome, a rare complication that occurs when fetuses share blood unevenly through the same placenta. The doctor told her that the fetuses were experiencing cardiac issues and that she should prepare for treatment the following day, Walsh said.

Her OB-GYN told her that, without immediate surgery, her twins had a high chance of perinatal death, and she could also die.

Both doctors referred Walsh to a fetal surgeon about four hours away, describing him as an expert on the condition.

As Walsh prepared to leave, she received a call from the surgeon's practice, the Fetal Institute. Walsh said a billing representative told her that before surgeon Ruben Quintero would see her, she needed to pay in full for the consultation, surgery, and postoperative care — a total estimate of $15,000.

Although Walsh had insurance, the biller said the surgeon was not in any private insurance networks nor did he offer payment plans.

"I burst into tears," Walsh said. "’I don't want to lose these babies.’"

Her mother agreed to give her money, and Walsh also called her insurer, who advised her to apply for a waiver that could allow them to reclassify the care as in network.

Late Wednesday, Walsh and her husband checked into a hotel near the practice's office in Coral Gables. The next morning, she handed her credit card and then her mother's credit card to the clerk at the Fetal Institute. Quintero said her case had advanced to stage 3, meaning there were problems that could cause heart failure in one or both fetuses.

He performed surgery later that day at a hospital about 90 minutes away. On Friday morning, she traveled back to his office for a follow-up. In the following weeks, she had two more consultations.

About five weeks after the surgery, Walsh gave birth to twin girls. They were premature but otherwise healthy.

Then she waited for her insurance reimbursement to come.

The Patient: Sara Walsh, 39, is covered by Blue Cross and Blue Shield of Texas through her employer, a national newspaper publisher.

Medical Service: Fetoscopic laser surgery for treatment of twin-to-twin transfusion syndrome, as well as pre- and postoperative evaluations and X-rays.

Service Provider: The Fetal Institute in Coral Gables, Florida, a practice that specializes in treating rare pregnancy complications.

Total Bill: $18,610 over multiple visits for surgery; pre- and post-surgical consultations; and two follow-up consultations for potential complications that didn't ultimately require more treatment. Walsh ended up putting $14,472.35 on her and her mother's credit cards. Her health plan eventually paid the Fetal Institute $5,419.44. Walsh was later partially reimbursed but ultimately paid more than $13,000 out-of-pocket.

What Gives: Walsh's case falls into a gray area of medical billing between emergency and elective care. Despite being insured, Walsh paid most of the full charges upfront and out-of-pocket for care that three doctors said she urgently needed to save her twins. And she knew the surgeon was an out-of-network provider.

Within 20 hours, Walsh gathered the thousands of dollars she was told she needed to pay before the surgeon would meet with her and prepared to undergo surgery in an unfamiliar hospital. "That 20 hours was just insanity," she said.

When Walsh called BCBS before her procedure, a representative told her that Quintero was in its network at a few facilities but not at his private practice, where he would evaluate her. Laura Kersey, a billing representative with the Fetal Institute, confirmed to KFF Health News that the practice accepts Medicaid — which covers nearly half of all births in Florida — but does not contract with private insurance.

"Our highly specialized practice sees patients from across the globe," Quintero said in a statement to KFF Health News. "It would be impractical to join all health plans. If any patient is unable to pay in full for a procedure, we offer them CareCredit or an alternative payment plan, on a case by case basis."

Neither option was available to Walsh. Approval for CareCredit, a medical credit card, would not have come in time for her next-morning procedure. Walsh said the Fetal Institute denied her request to pay half the bill upfront and the rest over time.

Kersey said requiring upfront payment is the Fetal Institute's "normal practice." She said they are transparent about their billing practices and disclose them to potential patients ahead of time. If someone cannot pay, she said, the Fetal Institute sends the person back to the referring physician to find another option.

Walsh said the BCBS representative advised her to complete a waiver intended for patients who receive urgently needed care from an out-of-network provider when it is not feasible to see an in-network provider. Walsh did not have the days or even weeks needed to undergo the insurer's formal preauthorization process, which could have told her in advance whether BCBS would cover the claim.

Walsh and her mother had paid the Fetal Institute nearly $13,000 related to her surgery, hopeful that BCBS would reimburse them.

In the weeks before Walsh gave birth, the specialist in Winter Haven sent her back to Quintero twice. Both times Quintero evaluated Walsh and sent her home without further treatment. She paid nearly $1,475 more for those visits.

Walsh said she had trouble getting all the documentation BCBS said she needed. In early November, she received the letter of medical necessity explaining the diagnosis.

The letter, signed by Quintero, said that twin-to-twin transfusion syndrome, when left untreated, results in pregnancy loss in 95% of patients.

But Walsh's situation didn't count as the type of emergency that could have qualified her for federal billing protections, said Erin Fuse Brown, a law professor and the director of the Center for Law, Health & Society at Georgia State University.

Walsh sought care that was "knowingly out of network, even though there was a figurative gun to her head," Fuse Brown said, referring to the potential loss of her twins or even her own life.

The federal No Surprises Act, which took effect last year, months after Walsh's surgery, protects patients who receive emergency services inadvertently from out-of-network providers and only in certain settings — particularly emergency departments and urgent care centers. It also covers nonemergency services received from out-of-network providers, but only at in-network facilities.

Federal laws requiring public access to emergency services apply only to hospitals, not individual providers in their offices, Fuse Brown said. Physicians generally can refuse new patients and charge what they want, if they are transparent about costs, she added.

"It's not a surprise medical bill if it's not a surprise," Fuse Brown said.

Only about 30 to 40 hospitals nationwide can perform fetoscopic laser surgery to treat twin-to-twin transfusion syndrome, Yale Medicine estimates.

Walsh said the specialist who referred her for a next-day surgical appointment gave her just two options for providers in the region, only one of whom practiced in her state. That was Quintero, who is renowned for his work on the condition. He is credited with pioneering the procedure Walsh needed and, with his colleagues, also developed a way to assess the condition's severity, known as the Quintero staging system.

But it turns out there was another option in Florida. Neither the specialist nor BCBS told Walsh about the possibility of getting care at the University of South Florida, she said. At the time, USF was the only other facility in her state that could have performed the procedure, according to Alejandro Rodriguez, a maternal-fetal medicine physician and an assistant professor at the USF Health Morsani College of Medicine in Tampa. Rodriguez said that USF accepts private insurance, Medicaid, and Medicare and doesn't require patients to pay upfront for care.

"There was no mention of shopping around," Walsh said. And with her doctors telling her the lives of her children — and potentially her own — were urgently at stake, she said it seemed her only option was to pay up.

"No parent should face the choice of 'How much money can I raise in the next 12 hours and is it enough to save the lives of my children?'" Walsh said.

Walsh has spent more than a year trying to get reimbursed by her health plan, repeatedly explaining her complicated case as representatives tried to sort out the proper billing codes for the rare, newer treatment. "No one understood how a doctor charged me more than $10,000 upfront to treat me," she said.

Walsh also reached out to a medical advocate, who she said concluded that Quintero had billed correctly.

Walsh's insurance covered Wellington Regional Medical Center, the in-network hospital where Quintero performed the procedure.

The Fetal Institute also filed claims for Walsh's care with BCBS, telling her they were filing on her behalf. BCBS processed the claims — including for Quintero's surgical services at the in-network hospital — as out-of-network care and reimbursed Walsh for just a fraction of the more than $18,000 charged.

Her "explanation of benefits" documents stated that Walsh was on the hook for the balance between what Quintero's practice charged and the $5,419.44 that BCBS paid.

Walsh said BCBS covered her pregnancy-related visits to other, in-network providers, adding that her plan fully covers all diagnostic and laboratory maternity care.

In early 2022, the Fetal Institute forwarded Walsh a check for about $1,282. According to the practice's records shared with KFF Health News, the check corrected an overpayment on the full charges, totaling $18,610 — which Walsh's payments and BCBS' reimbursements had together fulfilled.

Walsh said she had not received any other reimbursement.

BCBS declined to comment on Walsh's case, citing privacy concerns even though Walsh waived federal health privacy protections, which would allow the insurer to speak to a reporter about the case.

After a KFF Health News reporter contacted the insurer, Walsh said, a BCBS representative called to inform her that her claims had been "escalated," but eventually determined that the reimbursement was "appropriate" because the provider was out of its network.

The insurer said that the full amount of her balance doesn't apply toward out-of-pocket maximums in her plan.

The Takeaway: Federal billing protections are not designed to protect patients who choose out-of-network care, even when they find themselves in an urgent situation with few options and little time for comparison shopping.

And often only a handful of specialized providers can treat rare conditions. While that dearth of options raises ethical questions about whether it is OK for a doctor to demand payment upfront for lifesaving surgery, it is legal to do so, experts say. Many Americans would be challenged to raise $15,000 overnight.

"The patient did everything she could," said Fuse Brown.

Worse, still, she said: When a patient pays upfront, there's little incentive for providers and insurers to negotiate a fair payment or even cooperate to help patients get reimbursement.

The case shows how consumer protections are still lacking in many situations. "This could still happen tomorrow," Fuse Brown said.

Bill of the Month is a crowdsourced investigation by KFF Health News and NPR that dissects and explains medical bills. Do you have an interesting medical bill you want to share with us? Tell us about it!