To study the effectiveness of the pain relief method of transcutaneous electrical nerve stimulation (TENS) for women who will undergo suction evacuation under conscious sedation for first trimester termination of pregnancy.

Suction evacuation is a minor gynecological procedure commonly performed at an outpatient setting for termination of pregnancy. Although it is a simple surgical procedure lasting 5-10 min and can be done under various methods of pain control, 78-97% of women still report at least moderate procedural pain, especially during injection of paracervical block, cervical dilation, suction aspiration and postoperatively with uterine cramping. In addition, those pharmacological analgesic methods are often associated with numerous adverse effects and cannot be applicable to all women.

The transcutaneous nerve stimulation (TENS) method is commonly used to treat labour pain. It is an inexpensive, quick, easy to use and noninvasive pain relief method. A recent study by Lison et al. on TENS for office hysteroscopy demonstrated a significant decrease in pain scores when compared to control and placebo groups.

The rationale of TENS lies in achieving pain reduction when electric stimulation alters the nociceptive transmission in the dorsal horn of the spinal cord; this means the electrode has to be adequately applied in the right receptive field of the body to achieve pain control. For the setting of TENS there is evidence supporting superior pain relief by random high frequencies TENS over fixed frequency. Increasing the pulse duration to above 250 microseconds also produces better analgesics effect.

In suction evacuation, the nerve roots of T10-L1 and S2-S4 becomes relevant as they correspond to the nerve supply to the whole uterus and cervix. Lison et al placed electrodes at these levels parallel to the spinal cord in their study and have instructed their subjects to increase the TENS intensity to the maximum nonpainful level, allowing further increase when their stimulus perception decrease as a result of nerve accommodation.

Its use in suction evacuation however, remains undetermined as there is no published study in this area.

Inclusion Criteria:

• Chinese aged 18 years or above and mentally competent
• Up to 12 weeks gestation on the day of STOP
• Size of the uterus on pelvic examination compatible with estimated duration of pregnancy, or dating confirmed with ultrasound scan
• Normal general and gynecological examination

Exclusion Criteria:

• Skin damage or allergy at site of TENS pads application
• Previous experience with TENS
• History of pacemarker insertion
• History of severe respiratory or cardiac disease
• Severe and recurrent liver disease
• Allergic to lignocaine
• Myasthenia gravis
• Psychiatric conditions requiring medication
• Disorders that constitute contraindications to use of prostaglandins

Women who has up to 12 weeks gestation on the day of STOP

After the written informed consent is obtained, subjects will be randomly allocated into one of the two groups: (a) the active TENS group and (b) the placebo TENS group.