Low doses of inhaled analgesics can safely reduce pain during the early stages of labor, according to a new review of the evidence.

Researchers found women given either nitrous oxide - also known as "laughing gas" - or a group of drugs known as flurane analgesics reported lower pain than those who breathed in oxygen only or didn't use a face mask during labor.

Epidurals are far more commonly used for labor pain than inhaled drugs, researchers said - but they can also come with more side effects, and not all women want such strong medication.

"We would like women to have more choices for non-invasive methods if they wish," said Trudy Klomp, the lead researcher on the new review and a midwife from VU University Medical Center in Amsterdam.

"When women want to have some pharmacologic pain relief in labor, we think we must give them the choice for this form of pain relief, the inhaled analgesic," she told Reuters Health.

There are limitations to inhaled pain relievers, however.

Flurane derivatives must be administered by a trained professional in precise doses, Klomp said, because they can knock women out if too much is inhaled.

Researchers also haven't figured out whether doctors and midwives who use the analgesics on many of their patients have any long-term side effects from breathing in the gases regularly.

"The main barrier to use is the pollution that it causes and, if not properly used it may be a hazard to health care providers," Dr. Stephen Halpern, head of Obstetrical Anesthesia at Sunnybrook and Women's College Health Sciences Centre in Toronto, told Reuters Health in an email.

Halpern, who wasn't involved in the new study, said his hospital has a room set up with special ventilation for use of nitrous oxide.

But many other hospitals, including the vast majority in the United States, don't have those types of facilities and don't offer women the option of inhaled analgesics, according to Klomp.

Taking the edge off

She and her colleagues analyzed 26 studies with a total of almost 3,000 women in the early stages of labor (before they started pushing).

Both nitrous oxide and flurane derivatives were tied to lower pain intensity during labor on a 100-point scale, researchers reported this week in The Cochrane Library.

Women who used flurane derivates rated their pain 14 points lower than those who were given nitrous oxide - but nitrous oxide was still better than nothing for pain relief.

On the other hand, those who were given nitrous oxide for pain also reported more vomiting and dizziness than women who didn't get analgesics.

There was no difference in the chance women would need a Cesarean section or have an assisted vaginal birth based on whether or not they were given either type of inhaled pain reliever.

Klomp said women who use inhaled analgesics still feel some pain during labor, but it's tamped down. As Halpern explained, nitrous oxide can "take the edge off" labor-related pain.

Other options for non-invasive pain relief include acupuncture, massage and water immersion.

"There are also women who don't want to feel any pain at all, and when you don't want to feel any pain at all, the first method is an epidural," Klomp said.

But epidurals can make labor last longer, and women may need to take additional medication to promote contractions after getting the injection. Epidurals also raise the risk of both moms and babies running a fever, according to Klomp.

She said pregnant women should discuss their pain-relief options with their doctor or midwife. But most will have to go out of their way to ask for an inhaled analgesic if they want one, she added - and for many outside of the UK and Canada, it simply won't be an option.