Study on Fewer Tears (SOFT) - The Effect of Local Anesthesia on the Incidence of Perineal Tears in the First Vaginal Birth

Introduction Perineal tears are the most common complications of vaginal birth. Severe tears can cause long-term physical and psychological morbidity. Preliminary observations suggest that pudendal block and perineal infiltration with local anaesthesia may relax the pelvic floor muscles, reduce pain, and facilitate a more controlled pushing phase. The SOFT study investigates whether local anaesthesia during the second stage of labor decreases the incidence of perineal tears, including sphincter injuries, in women with their first vaginal birth (non-instrumental).

Materials and Methods Data collection for a prospective observational study is ongoing at Danderyd University Hospital. The study documents perineal protection techniques and the incidence of perineal tears in women with their first vaginal birth (non-instrumental). Findings from this preparatory study will guide the design of a randomized, double-blind, controlled trial to evaluate whether pudendal block and perineal infiltration with mepivacaine or placebo have a protective effect on perineal trauma.

The aim is to include 1,350 participants in this observational study. Midwives complete a case report form indicating the use of manual perineal protection, fetal presentation and position, the duration of the second stage, the detailed degree of perineal tear, pain management during the pushing phase, and the need for local anaesthesia during suturing. The full analysis will evaluate associations among perineal protection techniques, local anaesthesia, and the incidence and severity of perineal tears.

Inclusion criteria

• Pregnant individuals giving birth.
• Live fetus/fetuses.
• Gestational week 34 or more at birth.
• First vaginal birth, i.e., individuals with prior cesarean section can be included.

Exclusion criteria

• Intrauterine fetal death or stillbirth.
• Labor resulting in cesarean section or instrumental delivery.