An original article for MidwifeInfo.com by Nancy Sullivan, CNM, MS, FACNM

TENS (Transcutaneous electrical nerve stimulation) is a method of electrical stimulation used to provide a degree of symptomatic pain relief by specifically exciting sensory nerves. TENS units consist of a small machine with controls (about the size of a cell phone or Palm pilot), connected by lead wires to electrode pads placed appropriately to alleviate various types of pain. Some units, such as the LadyTENS, are battery-operated and small enough to carry in the hand or in a pocket. Most TENS units operate in two modes, a burst or pulse mode for chronic or low-level pain, and a constant mode for acute, short-lived pain (such as a labor contraction). When turned on, the TENS unit delivers a tingly, buzzing sensation to the area under the electrodes. It is thought that this sensation works in two ways to alleviate labor pain: it causes your body to release natural pain killers called endorphins, and it acts as a gateway, blocking deeper pain messages from travelling to your brain.

Does TENS have side effects? Can it cause problems for my baby?

TENS is non-invasive and has few side effects when compared with drug therapy. The most common complaint is an allergic type skin reaction (about 2% of patients) and this is almost always due to the material of the electrodes, the conductive gel or the tape employed to hold the electrodes in place.

Does TENS work?

TENS will not completely eradicate or take away labor pain in the way that an epidural does. Like hydrotherapy, relaxation and breathing techniques, and narcotic analgesia, TENS can lessen the pain and make it easier to tolerate. For women who want to make every effort to avoid pharmacologic pain relief (epidural or narcotic), TENS is an option that may help. Used in combination with other methods by a motivated woman, it is even more likely to do this. For women who think they may want an epidural when labor is intense, TENS can be helpful to get through the early labor until the point when it is appropriate to have an epidural placed.

Success is not guaranteed with TENS. In several reviews of the research literature, no study was found that recorded any difference in pain intensity or pain relief scores between TENS and controls (women who did not receive TENS) during labor. In 8 of 10 reports, it was recorded that women required additional analgesic interventions, that is, other methods of pain relief in addition to TENS. For more details, see the Bandolier review at http://www.jr2.ox.ac.uk/bandolier/booth/painpag/Acutrev/labour/AP001.html or read the article in its entirety: Carroll D, Moore RA, Tramèr MR, McQuay HJ. Transcutaneous electrical nerve stimulation does not relieve labour pain: updated systematic review. Contemporary Reviews in Obstetrics and Gynecology 1997; Sept:195-205.

Interestingly, a Cochrane systematic review did find high-frequency TENS to be helpful for dysmenorrhea or painful cramps with menstruation. See Proctor ML, Smith CA, Farquhar CM, Stones RW. Transcutaneous electrical nerve stimulation and acupuncture for primary dysmenorrhoea (Cochrane Review). In: The Cochrane Library, Issue 4 2002. Oxford: Update Software. Perhaps if studies of TENS to alleviate labor pain were focused on early labor, they would find a more positive result.

What do women who have used TENS during labor say?

Women who have commented anecdotally on the use of TENS (comments can be found on the Gentle Birth and Baby Centre web pages) agree that it is more useful for early labor, and ceases to be helpful in the second stage when the mother is pushing the baby out. Some typical comments follow:

"I found TENS an absolute God-send and would use it again like a shot. It got me through most of my labour until transition without much else and I found it pleasant to use. I want one for period pain but they cost too much! :-( My friend used hers for post-Caesarean pain to great effect, and it's also good for coping with after-pains. Most of the women I've spoken to, who used it first time, say they would absolutely use it again."

"I used a TENS machine during my labor. I borrowed it from a British friend who used it for all her labors. She benefited greatly from it. I found it very helpful up to a certain point. You hold a little device that you push if you want another "shot" of tensing. When I was at the last point of active labor it started annoying me, so I pulled it off. But until that point it really helped (this was my third baby so I had done two before without any TENS). It especially helps with posterior birth because it really relieves backache. You have to take it off if you want to take a bath or shower, however, and you have to make sure you stick the little pads on exactly the right places on the back."

"I was using a TENS unit for back pain while I was pregnant and decided to try it during labor. I had an unmedicated labor that lasted about 29 hours. Most of it wasn't so bad. I went into labor Saturday afternoon, put on the TENS until Sunday morning and wore it until I got to transition. At one point I figured it wasn't helping because I was still feeling the contractions and they were pretty tough but when I turned it off I *KNEW* it had been helping! The contractions were much stronger feeling and hurt more in my back when I turned it off. I turned it back on and left it until the tingling started to annoy me. At that point I was very near pushing and I don't think it would have helped much then. The pushing contractions were much stronger and were in a totally different place that the labor contractions. Anyway, I loved mine and I plan to use it again!"

"I used tens with my first child 3 years ago and found it effective for the first part of labour - its a strange sensation and a good distraction. it only works up to a point though, i will be using it again when my 2nd baby is due at the end of feb 2001."

"I have given birth thirteen times (yes, thats 13 times!) and used a Tens machine for one birth and an epidural with one and nothing for the other eleven.The tens machine worked immediately.... I would say that the pain relief was maybe three quarters as good as the epidural. Pretty impressive to me given the low cost and apparent lack of side effects. Although the epidural was unquestionably effective, it does have its own set of possible risks, and my baby did not breathe spontaneously at birth. He had an apgar of 4 at one minute. Everyone insists that the epidural doesn't cause this effect, but I wonder, since my daughter, my sister-in-law, and two neighbors all had babies who needed resucitating at birth following epidurals."

Not all comments were positive. One woman said,

"I don't think that it worked, in fact it seemed to have the opposite effect for me, when I felt a contraction and pushed the button the electrical impulse seemed to cause the contraction to get stronger so I gave in and moved on to gas and air (which rocks!!)."

How do I find a TENS unit to use during my labor?

Some midwives or doulas have a TENS unit that they can rent to you. Some hospitals have TENS units, usually for the physical therapy department, that you can request while you are a patient. In the U.K., there are a number of websites that will hire a TENS unit, including BabyCare TENS and Pulsar Tens. A new company that works closely with midwives in the U.K. is Maternity TENS Hire. TENS units can also be hired from most Boots Pharmacies. In the U.S., it is harder to find a TENS unit for rent; some hospitals rent TENS units through their physical therapy or rehabilitation departments, and there are some websites that rent TENS units. If you have trouble locating a source, email me.