The TENS machine works by applying small electronic pads to your back. These pads will send electrical impulses which will in turn stimulate nerve cells that will interrupt the pain signals from the uterus and cervix from reaching the brain. By introducing a different sensation at the same time as the contraction, the brain has to divide its attention. By doing this, the intensity of the painful stimulus is diminished.
Don’t expect a TENS machine to take the pain of labour away. But, nothing really takes all of the pain away with the exception of an epidural and even that is not 100% guaranteed to work. The TENS machine is a wonderful tool to help you get through the toughest part of labour.
It is important for you to familiarize with the TENS machine before your birthing time. That is why it is recommended for you to have it at your home at least 1 week before you due date.