Ra﻿pid contractions left Anna Jaeger desperate for something more than the distraction of the jacuzzi during her slowly progressing labor with her first child.

Hoping to retain some sensation and avoid an epidural, she turned to an analgesic option available to few U.S. women -- nitrous oxide, better known as laughing gas.

"It was wonderful," she said, chuckling as she recalled the relief it brought. "I told the anesthesiologist I loved her, it helped that much."

That's a pretty typical response, according to nurse midwife Judith Bishop, CNM, MPH, who assisted with the delivery at the University of California San Francisco Medical Center.

UCSF is one of only three centers in the country that offer nitrous oxide during labor and delivery. But that may be changing as a grassroots movement driven by nurse midwives pushes to give women an intermediate option short of an epidural.

Pain Relief That's 'Good Enough'

Obstetric analgesia has a limited range concentrated at the two extremes: nonmedical tools like massage and hot tubs that make women more comfortable and epidural infusions that block all feeling below the administration site.

Opioid painkillers are also available but typically don't do much for labor pain, noted Suzanne Serat, CNM, MSN, a nurse midwife at Dartmouth-Hitchcock Medical Center in Lebanon, N.H.

"In studies that look at how much pain relief there is from different tools, tubs rate higher than narcotics," she explained in an interview with MedPage Today.

Nitrous oxide may bridge that gap with modest pain relief.

"[Women] won't say it makes a tremendous dent in their pain," Bishop told MedPage Today, "but it often provides enough distance and relief for the quintessential response 'It still hurts but I don't care.'"

Specialized equipment fixes the oxygen-to-nitrous oxide ratio at 50/50, and the woman holds the mask in her hand, controlling when and how much anesthetic she gets.

These measures ensure that the gas never becomes anesthesia, as it does when used in the operating room or dental office, and eliminates concerns about oxygenation for mother and baby, Bishop noted.

Because the body doesn't metabolize nitrous oxide, its quick-on, quick-off effect makes it a flexible tool in the delivery room, added Serat, who is part of a team evaluating its potential use at Dartmouth.

Women can get up to go to the bathroom, for example, whereas an epidural tethers them to the bed, she noted.

Nitrous oxide also provides a quick option for women progressing too rapidly through labor to get an anesthesiologist in to administer an epidural or for those who are planning a "natural" unmedicated birth but who hit a rough patch and need some relief, Bishop pointed out.

Nitrous oxide may hold the most promise for free-standing birthing centers or those that don't have an anesthesiologist available 24-7, noted Craig M. Palmer, MD, of the University of Arizona in Tucson and chair of the obstetric anesthesia committee for the American Society of Anesthesiology.

Push for Nitrous Oxide Starts Small

For all these reasons, nitrous oxide has been gaining a following among nurse midwives, and the burgeoning interest has no greater cheerleader than Judith Rooks, CNM, MS, MPH, the former head of the American College of Nurse Midwives and professor emeritus at Oregon Health & Science University in Portland.

"It was so striking to me that women in other countries had this choice and women in the U.S. didn't," she told MedPage Today.

In fact, the majority of women laboring in England and Scandinavian countries use nitrous oxide and it's used in about one in five deliveries in Canada. But the gas never really caught on for labor analgesia in the U.S., with epidurals taking over instead, Rooks explained.

She started writing articles about the use of nitrous oxide in midwifery journals in 2007; they drew considerable interest and an Internet list serve resulted.

"I want to expand access," Rooks told MedPage Today. "If epidurals weren't available I would want to expand access to them. I believe women should have a choice. I focused on nitrous oxide because it's missing from what's available to women in the U.S."

And that is a message that resonates with midwives and pregnant women alike.

"The resurgence is being driven by midwives," Serat said. "We spend lots of time with women in labor. Lots of time. ... It's just nice to have as many tools as you can possibly have."

Consumer interest is likely to drive the rest of the progress, once hospitals see nitrous oxide as a factor that can give them an edge in attracting deliveries to their center, Bishop noted.

That's been the case at Vanderbilt University Medical Center, noted obstetric anesthesiologist Sarah Starr, whose center, in Nashville, Tenn., has purchased the equipment and is on the threshold of becoming the fourth to offer nitrous oxide for labor.

"In our department there was an initial thought of why would anybody want anything other than an epidural because an epidural obviously provides superior pain relief," Starr told MedPage Today. But "we have a very great patient interest in it. Women are very interested in having different options."

Not Competition, Just an Option

Nitrous oxide is no replacement for epidurals, Palmer cautioned in an interview supervised by ASA public relations staff.

"It's just not that great a pain reliever," he told MedPage Today. "Even in places that embrace it I think a lot of patients would say 'It's not working that well, now I'll have the epidural.'"

Other factors can come into play as well. In Anna Jaeger's case, for instance, she had to switch to an epidural to stop her premature pushing response that threatened to lead to a C-section.

"It's not one size fits all," Bishop said. "More choices is a good idea."

Labor pain differs from the sort managed in other areas of medicine, noted Bishop, who has become one of the nation's go-to experts on the subject because of the scarcity of obstetric experience with nitrous oxide here.

Women in labor know the pain is normal and going to come to an end, and not all of them want to lose all sensation of the birth, she explained.

"This is not throwing them scraps," Rooks argued. "Not everybody wants the same thing."

Rather than being a turf issue, obstetric anesthesiologists and nurse midwives have a common goal, according to Starr.

"We want to provide the safest and best care for all our patients," she said. "As an anesthesiologist, it has more to do with really coming to grips with the fact that just because something provides complete pain relief doesn't mean it's the best option for all women."

What's Stopping Acceptance

One major factor curtailing the fledgling field's momentum is the lack of infrastructure, noted Palmer.

"Most facilities simply aren't prepared to offer nitrous oxide for labor analgesia," he said.

The FDA has not approved the premixed oxygen and nitrous oxide tanks that are used in other countries, and the manufacturer of the fixed-ratio equipment used to mix the separate gases stopped production because of a lack of sales.

"Unfortunately Judith Rooks started this whole effort right at the time, unbenownst to all of us, that the company that made the only equipment for this purpose decided to stop making it," Bishop explained. "So we've had a big disconnect between interest and ability to institute it due to lack of equipment."

Starr's group at Vanderbilt had to resort to the secondary market for pre-owned machines.

That limitation may change any time now, though, according to Evan McAllister, CRT, whose company Nitrogesia in Double Oak, Texas, is awaiting the all clear from the FDA to put their nitrous oxide equipment on the market.

McAllister predicted that, in the most optimistic scenario, the gas-blending equipment could be ready for the waiting list of universities and other centers in a little as a month.

Another possible hang-up is concern over safety.

There's been no investigation into the effects of in utero exposure to nitrous oxide, and nitrous oxide exposure to allied health professionals often exceeds federal occupational safety limits, Palmer cautioned.

Those levels were set arbitrarily based on weak data from operating rooms in the 1970s, and prior studies that suggested a possible effect on time to get pregnant, Serat argued.

The professional exposure concerns can be addressed by use of masks that scavenge the nitrous oxide and periodically having nurses wear badges to monitor exposure, Bishop suggested.

But because even the efficacy data for pain relief with nitrous oxide is uniformly old, Starr said her group plans to study these issues once clinical use gets under way at Vanderbilt.

Dartmouth may wait to make its final decision on instituting nitrous oxide during labor until they see Vanderbilt's data and have more safety assurance in hand, Serat noted.

But that would be a mistake, Rooks argued, noting it will be years before that data comes in, whereas the European experience shows millions of women having used it without any evidence of problems.

"Just because people have been using it doesn't mean we know enough about its safety," Palmer countered.

It took a long time for epidurals to be accepted as safe, too, noted Rooks.

"Like anything it will come slowly," she predicted.

But grassroots acceptance is being helped along by women like Jaeger, who has been spreading the word among her pregnant friends.

"I think it's crazy that more hospitals don't use nitrous," she said.

This article was developed in collaboration with ABC News.