Yet epidurals bring an increased risk of delivery assisted by forceps or vacuum. The pluses and minuses mean that a woman's decision about pain relief is not clear-cut.
"Each woman will have to weigh how much it means to her to have a spontaneous vaginal delivery versus having more pain in labor," said lead author Dr. Millicent Anim-Somuah of the Liverpool Women's Hospital in England.
On a more positive note, mothers who receive the spinal injections are no more likely than others to require Caesarian sections or to suffer chronic backaches. Their infants are equally healthy soon after birth.
Epidural analgesia involves injecting a local anesthetic into the lower back to block pain impulses from the uterus and birth canal. Obstetricians introduced the technique in 1946, and 58 percent of American women now choose this form of pain relief during childbirth, according to the authors.
The review appears in the most recent issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The reviewers analyzed 21 studies involving more than 6,000 women. Most of the participants were in the United States, England and Australia.
"It's always been suspected that epidurals slow down your labor," said Anim-Somuah. The study confirmed that the nerve block lengthens the stage during which the mother must push the baby through the birth canal. This leads to greater use of medication to stimulate contractions and a 38 percent increase in risk of instrumental delivery.
The precise timing of the epidural injection may be an important factor, says Todd Liu, M.D., a fellow of the American College of Obstetricians and Gynecologists who practices in New Jersey.
"Should you get your epidural when you first feel a contraction or when you are in a strong labor pattern?" Liu asked. "I would guess that there would be a higher [Caesarian section] rate if epidurals are given too early."
Finally, there are certain "rare but potentially severe adverse effects" associated with epidurals, says the review. These include spinal cord injuries and permanent paralysis in the mother. These are so rare that incidence rates are currently unknown.
Randomized controlled trials like those included in Cochrane reviews are not well-suited to studying such uncommon events, said Anim-Somuah. "There should be some ongoing data collection as to whether these are occurring with epidurals."
For now, Liu said, "My usual recommendation is that if labor is going to be long (usually with the first baby) and labor pains are very intense ... then it is worth getting an epidural and accepting the potential risk."
A potential weakness of the review is that only one trial studied childbirth without any painkillers at all.
Health Behavior News Service
Contact Millicent Anim-Somuah at 011 44 151 708 9988.
Anim-Somuah M, Smyth R, Howell C. Epidural versus non-epidural or no analgesia in labour (review). The Cochrane Database of Systematic Reviews 2005, Issue 4.
The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit http://www.