RESUMEN
BACKGROUND: Severe perineal trauma (SPT) affecting the anal sphincter muscle complex is a serious complication following childbirth, associated with short-term and long-term maternal morbidity. Effective preventive strategies are still scarce. The aim of the Oneplus trial was to test the hypothesis that the presence of a second midwife during the second stage of labour, with the purpose of preventing SPT, would result in fewer injuries affecting the anal sphincter than if attended by one midwife. METHODS: In this multicentre, randomised, controlled parallel group, unmasked trial done at five obstetric units in Sweden, women were randomly assigned to be assisted by either one or two midwives in late second stage. Nulliparous women and women planning the first vaginal birth after caesarean section who were age 18-47 years were randomly assigned to an intervention when reaching the second stage of labour. Further inclusion criteria were gestational week 37+0, carrying a singleton live fetus in vertex presentation, and proficiency in either Swedish, English, Arabic, or Farsi. Exclusion criteria were a multiple pregnancy, intrauterine fetal demise, a planned caesarean section, or women who were less than 37 weeks pregnant. Randomisation to the intervention group of two midwives or standard care group of one midwife (1:1) was done using a computer-based program and treatment groups were allocated by use of sealed opaque envelopes. All women and midwives were aware of the group assignment, but the statistician from Clinical Studies Forum South, who did the analyses, was masked to group assignment. Midwives were instructed to implement existing prevention models and the second midwife was to assist on instruction of the primary midwife, when asked. Midwives were also instructed to complete case report forms detailing assistance techniques and perineal trauma prevention techniques. The primary outcome was the proportion of women who had SPT, for which odds ratios (ORs) and 95% CIs were calculated, and logistic regression was done to adjust for study site. All analyses were done according to intention to treat. The trial is registered with ClinicalTrials.gov, NCT0377096. FINDINGS: Between Dec 10, 2018, and March 21, 2020, 8866 women were assessed for eligibility, and 4264 met the inclusion criteria and agreed to participate. 3776 (88·5%) of 4264 women were randomly assigned to an intervention after reaching the second stage of labour. 1892 women were assigned to collegial assistance (two midwives) during the second stage of labour and 1884 women were assigned to standard care (one midwife). 13 women in each group did not meet the inclusion criteria and were excluded. After further exclusions, 1546 women spontaneously gave birth in the intervention group and 1513 in the standard care group. 1546 women in the intervention group and 1513 in the standard care group were included in the intention-to-treat analysis of the primary outcome. There was a significant reduction in SPT in the intervention group (3·9% [61 of 1546] vs 5·7% [86 of 1513]; adjusted OR 0·69 (0·49-0·97). INTERPRETATION: The presence of two midwives during the active second stage can reduce SPT in women giving birth for the first time. FUNDING: The Swedish Research Council for Health, Working Life and Welfare; Jan Hains Research Foundation; and Skane County Council's Research and Development Foundation.