Most of my clients use the TENS machine. See here for an explanation of how the TENS works. The use of the TENS is hugely under-rated for early labour, during active labour and I discovered recently that it is also awesome for post birth contractions! Many insurance companies will cover the cost of the TENS machine for labour and birth, so check with your provider before purchasing one. Midwife practices also have them often to rent. As far as I have observed in my practice the TENS never has negative affect. I have observed several times that the cases where I have had mothers not like it has been when the baby is in a posterior position. The TENS does, at a certain point AND usually during the transition phase, have less of an affect. If you take it off at that point the woman often notices and wants it back on again. This would suggest it is still having some affect.
The research on the tens machine for labour is not very extensive but here is a link to Evidence Based Birth for a summary of the research.
The TENS machine is also fantastic for induction. It is best to start using it simultaneously when the synthetic oxytocin is administered and it will trigger the bodies own hormonal system to produce endorphins, your natural pain relief. These are the hormones that are released to help you cope with labour. They are bypassed when synthetic oxytocin is administered into the blood via an IV. This is the reason many women experience induction as more painful than natural labour. The natural hormones are not helping with the process. The TENS can help with that or help tide a woman over until she can get medical pain relief.
This beautiful VBAC mama used the TENS machine to help her through a very long labour It supported her past that dilation point of her 1st birth, and onto a natural vaginal birth. If the TENS is only put on during active labour then the affect will be much less as the pain being experienced is usually already high.
Double natural pain relief. The TENS does not interfere with other pain relief options except for water of course. So getting your partner or doula to do the hip squeeze & having the TENS machine on is a great combination and can help even better against the use of medical pain relief. .