This study evaluates the effectiveness of the Transcutaneus Electric Nerve Stimulation (TENS) during the labour. TENS is a low frequency electrotherapy technique, analgesic type, generally used in musculoskeletal pathology.

The investigators will have three groups of participants to be administered the TENS, a different dose in two groups, while the third will correspond to placebo.

The hypothesis of the study is to verify if the TENS is effective as a non-pharmacological method in the relief of pain during childbirth

1. Background:

   Pain during labour is one of the most intense pain that many women could experience during their lives, and it can be influenced by the anatomical and physiological factors of the labouring women, and also, by their psychological experiences, as well as by cultural, social, and environmental factors.

   Neuraxial analgesia during labour is the most effective method for pain relief, but it appears to be associated with certain side effects, such as maternal hypotension, decreased uteroplacental perfusion, foetal bradycardia, fever, pruritus, an increased oxytocin requirement, a prolonged second stage of labour, a higher rate of operative delivery, and high costs.

   The use of non-pharmacological methods for pain relief includes a wide variety of techniques aimed at improving physical sensations and preventing psychoemotional perception of pain. Among the main nonpharmacological methods of pain relief at delivery is the application of Transcutaneous electrical nerve stimulation (TENS). Its application during childbirth is based on the Gait Control theory of pain of Melzack and Wall. According to their theory, the application of TENS reduces the excitability of the delta A and C pain fibers, thus reducing the amount of painful messages ascending the spinal cord. Activation of these fibers stimulates the release of natural pain inhibitors.

   Furthermore, many non-pharmacological methods of managing pain increase the satisfaction of women with their childbirth experience.

   TENS have used for labour analgesia and there are several studies which show its effectiveness. The effectiveness of TENS depends on the duration, frequency and amplitude of the stimulating current and the site of application of the electrodes. TENS can be administered by either dermatomal stimulation or by stimulation of acupuncture points for labour analgesia. In addition, all studies stated that it was safe and there was no side effects on the mother and the baby.

   This work was conducted to study the effectiveness of TENS on labour analgesia, maternal and fetal outcome using TENS by dermatomal stimulation technique. Thus, device will be used as follows:

   Through electrodes applied to the lower back, the parturient can control both parameters, the frequency and intensity of the low-voltage electrical impulses emitted from the TENS device. When applying to the lower back, the TENS unit emits electrical impulses which excite afferent nerves, and thus inhibit the transmission of painful stimuli arising from the uterus, vagina and perineum during labour. These electrodes are attached to the skin bilaterally at paravertebral positions T10 and S2.

   In the present study the investigators will use three equal devices (two different dose and one placebo) .They will be assigned a number that associate to each group of participants.

   Safety profile in the use of TENS:

   It is a non-invasive technique, easy to administer, without side effects or interactions with other drugs, it cannot produce toxicity in the tissue or cellular level.

   The current literature does not reflect any complications, either on the part of the pregnant woman and in the fetus, during the application of TENS in the labor phase.

   The use of TENS should be contraindicated in women whose gestational age does not exceed 37 weeks, women with pacemakers and water births. It should not be applied in the maternal abdomen, at any time during pregnancy or childbirth, to avoid stimulation near the fetal heart.

2. Objectives:

   Primary aim:

   • To know if the application of TENS is effective in reducing pain during childbirth.

   Secondary aim:

   • To determine the most effective dose in the use of TENS in pregnant women during labor.
   • To analyze the degree of satisfaction of the pregnant women who participate in the study.
   • To evaluate whether the use of TENS reduces the dose of the painkillers during childbirth.

3. Material and Methods:

This study is a triple blind randomized trial with concealed allocation, assessor blinding for some outcomes, and intention-to-treat analysis.

It was accepted by the Ethic Committee of the Hospital Complejo Hospitalario Universitario Insular Materno Infantil of Las Palmas de Gran Canaria, Canary Islands, Spain, with registration number CEIm-CHUIMI-2016/875.

3.1. Allocation: All participants will be recruited from a group of women admitted to the hospital. If the pregnant woman meets the inclusion criteria, she will be asked to participate in the study. If yes, they must sign the informed consent, approved by the same ethical committee of the hospital.

The assignment to each group was made through the website www.random.org to perform randomization. In addition, each group has a different TENS, which has the group number. Participants in all groups will receive all the other routine obstetric care.

3.2. Sample size determination: The sample size and power calculations were performed using the software GRANMO 7.11. Calculations were based on detecting differences of 2 units in a 10 numerical pain rate scale at post-data, assuming a standard deviation of 1.9, a 2-tailed test, an alpha level of 0.05, and a desired power of 80%. These assumptions generated a sample size of 63 subjects, 21 per group.

There is a specialiced nurse that will supervised the correct functionality every day. He will be responsible for resolving dispositive problems like low charge or insufficient electrodes.

Inclusion Criteria:

• Parturients with a low-risk pregnancy.
• A gestational age > 37 weeks.
• A single foetus.
• Cervical dilation of 4 cm.
• To be older than 18 years old.
• Visual deficit that causes difficulty to take the Visual Scale Analogue.

Exclusion Criteria:

• Refusal to take part in the survey.
• Failure to Sign Consent Form.
• Planned Cesarean.
• High-risk pregnancy.
• Present skin lesions in the area of the application of the electrodes.
• Pregnant with physical or mental handicap that prevents the application of the TENS device.
• Have implanted pacemakers or automatic defibrillators.

The participants will be pregnant women.