The goal of this clinical trial is to determine whether inhaled nitrous oxide can reduce pain and anxiety during cervical cerclage removal compared with standard care. Cervical cerclage removal is commonly performed in the outpatient setting during the third trimester of pregnancy and may be associated with discomfort and anxiety despite being a brief procedure.

The study will include pregnant women aged 18 years or older undergoing elective cervical cerclage removal at 36 weeks of gestation or later.

The main questions the study aims to answer are:

• Does inhaled nitrous oxide reduce pain during cervical cerclage removal?
• Does inhaled nitrous oxide reduce anxiety during the procedure?
• Does the use of nitrous oxide improve overall patient satisfaction during cerclage removal?

Researchers will compare women receiving inhaled nitrous oxide to those receiving standard care without analgesia, as routinely practiced in the participating institutions, in order to determine whether nitrous oxide improves pain control and patient experience during the procedure.

Participants will:

• Be randomly assigned to receive either inhaled nitrous oxide (50% nitrous oxide / 50% oxygen) or standard care without analgesic treatment during cervical cerclage removal.
• Undergo the procedure according to routine clinical practice in the participating centers.
• Complete questionnaires assessing pain and anxiety, including a visual analog scale (VAS) for pain and the State-Trait Anxiety Inventory (STAI).
• Have routine clinical data recorded from their medical records, including maternal vital signs and any procedure-related side effects.

Cervical insufficiency is a recognized risk factor for spontaneous preterm birth, which remains a major cause of perinatal morbidity and mortality worldwide. Cervical cerclage is an established intervention used in carefully selected patients to reduce the risk of preterm birth.

While cerclage placement is typically performed under anesthesia in the operating room, cerclage removal is usually carried out in the outpatient setting during the late third trimester of pregnancy. Despite being a brief procedure, many patients experience pain, discomfort, and anxiety during cerclage removal. Evidence regarding optimal pain management strategies for this procedure remains limited, and most patients currently undergo cerclage removal without analgesia.

Nitrous oxide (N₂O) is an inhaled gas with well-established analgesic and anxiolytic properties. It has a rapid onset and offset of action and a favorable safety profile. Nitrous oxide is widely used in obstetrics, particularly for labor analgesia, and has also been used for pain management during minor medical procedures. However, its use specifically for cervical cerclage removal has not been well studied.

This study is a multicenter randomized controlled trial designed to evaluate whether inhaled nitrous oxide reduces pain and anxiety during elective cervical cerclage removal. Participants will be randomly assigned in a 1:1 ratio to receive either inhaled nitrous oxide (50% nitrous oxide / 50% oxygen) during the procedure or standard care without analgesic treatment, as routinely practiced in the participating institutions. Randomization will be stratified by site and implemented using sequentially numbered sealed envelopes opened immediately prior to the procedure.

All procedures will be performed according to routine clinical practice in the participating centers. Maternal and procedural data will be collected from medical records, including procedure duration, maternal vital signs, and any reported side effects such as nausea, dizziness, or headache. Pain intensity will be assessed using a 0-100 mm visual analog scale (VAS), and anxiety levels will be evaluated using the State-Trait Anxiety Inventory (STAI). Additional outcomes will include maternal heart rate during the procedure and patient satisfaction with the procedure.

This trial aims to determine whether inhaled nitrous oxide can effectively reduce pain and anxiety during cervical cerclage removal. The findings of this study may provide evidence to support improved pain management strategies for this procedure and may contribute to enhancing patient experience during cerclage removal.

Inclusion Criteria:

• Age ≥18 years
• Women at ≥34 weeks of gestation
• Singleton or twin pregnancy
• Ability to understand, sign informed consent, and complete questionnaires

Exclusion Criteria:

• Triplet or higher-order pregnancy
• Contraindications to nitrous oxide use
• Fetal monitoring category 2 or higher
• Maternal body temperature >38°C
• Significant vaginal bleeding
• Severe preeclampsia
• Cerclage removal under general anesthesia
• Language or cognitive barrier
• Baseline pain >3 on VAS scale, prior to the procedure