Most women sustain some form of perineal trauma when giving birth vaginally. Perineal injuries are classified as grade I-IV. A first-degree tear only includes perineal skin or mucosa, whereas a second-degree tear includes muscles in the perineal body. A tear involving a part or the whole of the anal sphincter muscle complex is graded III-IV. Data from the Swedish National Birth Register show that 4% of first-time mothers suffered a tear affecting the anal sphincter. National registers in Sweden only collect data on severe perineal trauma affecting the anal sphincter but in a recent regional Swedish study 78% of the primiparous women experienced second-degree tears. The consequences of second-degree tears and severe perineal trauma are pain, dyspareunia, and an increased risk of symptomatic pelvic organ prolapse later in life. A severe consequence of perineal trauma is anal incontinence, mainly caused by tears affecting the anal sphincter muscle. However, second-degree tears may also lead to anal incontinence. This may be related to a lack of support from the perineal body due to poor repair. Furthermore, perineal trauma is known to be misclassified, with consequent under-reporting of injuries affecting the anal sphincter complex.

Risk factors for severe perineal trauma (grade III-IV) are giving birth vaginally for the first time, having an assisted vaginal birth, giving birth vaginally after a previous caesarean section, or giving birth to a baby that weighs more than 4000 g, and the risk increases with age. Some of the midwifery care methods used to prevent perineal injuries have been evaluated in clinical trials but there are still gaps in the investigator's knowledge. Even if scientific evidence is lacking for most of the preventive strategies used by midwives except for warm compresses held at the perineum, midwives believe that a slow and controlled birth is a key factor in prevention. Several studies indicate that a combination of strategies can be effective in preventing perineal trauma. Giving birth is a profound experience for the woman and her partner and an experience that has significance for the woman all her life. The second stage is considered to be the most stressful part of the labor for the woman and her unborn baby, and consequently also for the midwife. Despite this, there is still a lack of knowledge about how women experience the second stage and the methods midwives use to facilitate birth and prevent perineal trauma. Traditionally midwives have asked colleagues for a second opinion or to assist in complicated situations, or in obstetric emergencies. Recently a new clinical practice has been introduced in approximately 50% of the maternity wards in Sweden to reduce severe perineal trauma. This procedure involves two midwives attending the woman during the second stage of labor. The midwife responsible for the birth calls for the second midwife when the active phase of the second stage has started and the presenting part of the baby is visible. The second midwife observes the birth and can assist the midwife responsible for the birth if needed. An unpublished survey from one maternity ward in Sweden showed that most of the midwives appreciated this way of working but were uncertain as to whether it actually reduced the prevalence of severe perineal trauma. Furthermore, this clinical practice might have negative side-effects or unintended consequences. The maternity wards that practise this method have not increased the number of midwives. It could be argued that there is a risk that other women in labor will be left unattended for longer periods when two midwives assist at births. How midwives share the responsibility and communicate are factors that needs to be evaluated scientifically.

The objective of this trial is to evaluate whether collegial midwifery assistance during the second stage reduces perineal trauma grade III-IV.

Data from the National Birth Register show that 4.1% of first-time mothers suffered severe perineal trauma (OASI) in Sweden 2017. To be able to detect a reduction from 4.1 to 2.0% (50% reduction) with 80% power and a 95% level of significance, 1052 women in each group will be needed. The 50% reduction is based on regional figures after a change in practice and is therefore clinically significant. Allowing for a possible 40% drop-out rate including possible cases of obstetric emergencies where another midwife will be needed regardless of randomization, this will result in 2946 women in total. To ensure that there are no adverse side-effects of the intervention interim analyses will be performed every 6 months until the end of the trial. In the interim analysis, the distribution of the intervention and standard care will be estimated among women with no perineal tears, women diagnosed with a third- or fourth-degree tear (OASI), and neonatal outcome (apgar score at 5 minutes and arterial blood gas from the nuchal cord).

Women will be asked to participate in the trial when arriving to the maternity ward. The randomization will take place when the woman enters the second stage. It will not be possible to blind either women or midwives in this study. The participants will be randomly allocated (1:1) to the intervention group or to the standard care group. To allow for equal distribution between the groups, block randomization in blocks of ten (five to the intervention and five to the control group) will be used.

After the birth the tear will be diagnosed together with a midwife or an obstetrician who has not been involved in the birth. Tears will be sutured according to the guidelines at each participating study site. The midwife responsible for the birth will complete a questionnaire which will contain questions regarding the woman; labor and birth variables, methods of preventing perineal trauma, questions regarding the baby, diagnosis of the tear and how the tear was sutured. If a second midwife has been present during the second stage (intervention) the responsible midwife will also complete questions on the assistance she got from the second midwife and how this assistance was experienced. Data will also be retrieved from the participating women's records by using the local database of each study site. When the intervention has taken place the second midwife will also complete a questionnaire.

The women in the trial will be sent a questionnaire one month and one year after the birth. The follow-up questionnaire after one month will contain questions regarding their experience of the intervention and their experience of the methods used during the second stage and women's well-being (EPDS, Pain relief, sexual intercourse resumption, breastfeeding initiation), after birth.

For the one-year follow-up the following validated questionnaires will be used: Pelvic Floor Impact Questionnaire (PFIQ7), Pelvic Floor Distress Inventory - short form (PFDI-20), Pelvic Organ Prolapse/Urinary Incontinence Sexual Function Questionnaire (PISQ-12) Female Sexual Function Index FSFI, Edinburgh Postnatal Depression Scale (EPDS) and breastfeeding duration.