This is a prospective cohort study with an experimental design where an intervention is compared with standard care. The study was conducted at two maternity wards in Stockholm. Maternity ward 1 provides care to approximately 6,500 women/year whereas maternity ward 2 cares for approximately 4,100 women/year. Both wards provide care to women with low‐ and high‐risk pregnancies.
The primary outcome was perineal injuries, classified as second‐degree tears according to international standards 27, in addition using a new Swedish classification where vaginal tears with a measured depth of > 0.5 cm are considered second‐degree tears 28 because of the probability of a fascia defect. Secondary outcomes were the prevalence of no tear at all, severe perineal trauma affecting the anal sphincter complex, episiotomy, and the ability of the midwives in the intervention group to use the intervention.
Second‐degree tears are not registered in the national birth register in Sweden but examination of the local database of births for one of the maternity wards in this project revealed that 77 percent of the primiparous women had a vaginal and/or perineal injury, which is in line with previously reported prevalence 1, 29. A pretrial power calculation based on the assumption that the intervention would reduce second‐degree tears by 15 percent compared with standard care, indicated that at least 242 women were needed in each group to reach a statistical power of 80 percent at a 95 percent significance level (alpha). To ensure that enough participants were recruited to the study and taking dropouts into account, an additional 20 percent generated 291 women in each group.
The study included nulliparous Swedish‐speaking women, gestational age ≥ 37 + 0 weeks with spontaneous onset of labor or induction of labor. Cases of nulliparous women with diabetes mellitus (manifest or pregnancy‐induced), preterm birth ≤ 37 + 0, intrauterine growth restriction, female genital mutilation, multiple pregnancy, fetus in breech presentation, and stillbirths were excluded.
During the study period 1,773 nulliparous women fulfilled the study criteria (Fig. 1). The midwives were asked to write down their reasons for not including women in the study but most often forgot to do so. Reasons given for not asking women to participate were high workload, women not speaking Swedish (exclusion criterion), and failing to remember to ask women to participate.
The intervention is based on a theoretical framework of woman‐centered care 26 which consists of three parts (listed below) and is referred to as the MIMA model of care (an abbreviation for Midwives’ Management during the second stage of labor). The midwives in the intervention group were asked to use all three parts of the intervention during the second stage in all births they attended.

Spontaneous pushing: The woman feels a strong urge to push and follows the urge but does not put on any extra abdominal pressure. The midwife will if needed assist the woman to accomplish a controlled and slow birth of the baby by encouraging breathing and resisting the urge to push during the last contractions 30.

Flexible sacrum positions: Birth positions with flexibility in the sacro‐iliac joints, thereby enabling the pelvic outlet to expand (kneeling, standing, all‐fours, lateral position, and giving birth on the birth seat) 20.

Using the two‐step principle of head‐to‐body birthing technique if possible 18. With this technique, the head is born at the end of a contraction or between contractions and the shoulders are born with the next contraction.

Standard care during the second stage of labor is sparsely recorded by midwives in Sweden and there are no national guidelines about birth position, pushing methods, or whether certain methods of manual perineal protection should be performed. Hence, the management of the second stage of labor depends on the assisting midwife's experience, knowledge, and preferences. The assumption derived from reviewing research and clinical experience is that standard care for primiparous women consists mostly of directed pushing and semi‐recumbent birth positions 17. Furthermore, midwives often prefer to assist the woman to birth the baby's head and shoulders in one contraction because of fear of endangering the child 31.