The results of this study show that women assisted in the “PPA model of care”, when compared to the “Standard of care model”, had a significantly higher proportion of induced or spontaneous labor and vaginal birth, but without significant differences in the proportion of women assisted in collaborative work during labor and in the proportion of vaginal births assisted by nurses.
When compared to a national survey on pregnancy and childbirth carried out between 2011 and 2012, there was an increase in the proportion of women assisted in collaborative work during labor in private hospitals, almost twice as much as that observed previously (51.9% vs 28.7%) . In addition, although the proportion of women assisted in collaborative work has not shown a significant difference in the two models of care, in absolute numbers more women benefited from the assistance provided by nurse-midwives in the “PPA model of care”, as the proportion of women in labor in this model of care was higher than in the “Standard of care model”.
The use of recommended practices among women assisted in collaborative work was high in both models of care, which is consistent with the available evidence on childbirth care provided by nurse-midwives [14, 15, 20]. The only practice with intermediate implementation in the “PPA model of care” was the use of epidural analgesia for pain relief, but its evaluation was limited by the lack of data related to the woman's request for analgesia, and it is not possible to verify whether the lower use was due to not requesting analgesia, insufficient provision of this method or both.
However, data prior to the implementation of the PPA quality improvement project are not available, and it cannot be ruled out that the PPA has influenced care more broadly, and not only in the population exposed to the project, increasing the use of recommended practices throughout the entire population of the hospital. In addition, there was a significant difference in the use of some practices, for example, less use of “enema on admission”, and greater presence of “companionship during labor” and “monitoring of labor progression” in the “PPA model of care”. This suggests that the assistance in collaborative work may have been improved by the PPA, resulting in a greater offer of recommended practices, which is already considered satisfactory for most of the women assisted in collaborative work in the “Standard of care model”.
Among all the women in the “PPA model of care” who were assisted either in collaborative work or only by doctors, there was a satisfactory or intermediate use of recommended practices in labor. This is consistent with the results of a study that compared the care provided in hospitals participating in the PPA with private hospitals evaluated in the study “Birth in Brazil”, which showed a significant increase in the use of recommended practices during labor in women assisted in the PPA in hospitals, although not all of them reached a satisfactory level . In the comparison between assistance in collaborative work and that provided only by doctors, there was greater access to “oral fluid and food”, “maternal mobility and position”, “monitoring of labor progression”, and “non-pharmacological methods” and “epidural for pain relief” among women assisted in collaborative work. These results are in line with other national [15, 20] and international  studies, where the collaborative work during labor was associated with greater use of recommended practices that can offer greater comfort to women and favor a more positive experience of labor .
There was a high use of non-recommended practices regardless of the model of care (PPA or standard of care model) or the professional who provided care during labor (collaborative work or doctors), with only “enema on admission” and “perineal/pubic shaving” showing satisfactory results. Such findings are similar to a previous study that encountered the routine use of practices such as venous infusion and use of amniotomy and oxytocin during labor by both doctors and nurses . However, they differed from a previous study carried out in four public Brazilian hospitals, where the collaborative work was associated with reduced use of amniotomy .
The observed result of satisfactory use of recommended practices, although there is still excessive use of non-recommended practices, both in the “PPA model of care” and in the “standard of care model”, suggests a greater facility of incorporating recommended practices than abandoning practices that were once used routinely but are no longer recommended. An English cohort study, which compared maternal and perinatal outcomes and labor interventions according to birthplace, concluded that women assisted in the hospital setting are exposed to more interventions than those who choose other types of birthplace, such as birth centers and home births . Institutional factors such as structure and physical spaces, and rigid protocols, as well as aspects related to the culture and organization of the health system can hinder or facilitate a less interventionist practice by health professionals in general [18, 20, 30].
The higher proportion of vaginal births in the PPA model of care is an important result, but it should be analyzed with caution, as we found that women in the PPA were younger, had lower frequency of pregnancy complications, and most of them belonged to Robson Groups 1 to 3, where lower rates of CS are expected. In the “Standard of care model”, most women belonged to Robson Groups 5 and 2, which are the groups that contribute most to the rate of CS in Brazilian private hospitals . However, other studies suggest that childbirth care practices changed after the implementation of the PPA, and that the increase in the proportion of vaginal births was not the result of a more overall change in the private sector [17, 28].
The proportion of vaginal births assisted by nurse-midwives was very low, only 2.2% in the “PPA model of care”, without a significant difference between the two models of care. Results of a national study carried out between 2011 and 2012 also showed low participation of nurse-midwives in childbirth care: of the 48% of vaginal births in public and private services, only 16.2% were assisted by nurses . The Northern and Southeastern regions recorded the highest frequency of childbirth assistance by nurses, but for different reasons. While in the Northern region the greater participation of nurses is related to the higher occurrence of non-hospital births, which are also assisted by traditional midwives, and the lack of medical professionals, in the Southeastern region the greater role of nursing is due to the implementation of humanization processes of care in the pregnancy-puerperal cycle that has occurred since the 1990s, with the inclusion of nurse-midwives in the childbirth model of care, mainly in public services [4, 13, 15, 32].
More favorable results were found in an evaluation conducted between 2016 and 2017  in Brazilian public hospitals that are part of the “Stork Network” , a policy that aims to ensure women the right to reproductive planning and the improvement of humanized care during pregnancy, childbirth and the puerperium in public services of the Brazilian Unified Health System. In this assessment, it was found that more than a third of vaginal births were assisted by nurses, in contrast to the 16.5% found in public maternity hospitals between 2011 and 2012 . Despite these advances, the authors emphasize that the childbirth care provided by nurses is still insufficient, which they attribute to barriers and difficulties for the implementation of childbirth care by nurse-midwives that can be attributed to the still insufficient investment in the training of these professionals, to the low salaries, and to the low hiring rate of nurse-midwives by public hospitals and an even lower one by private hospitals. In addition, the authors point out the obstetricians’ resistance to collaborative work and the disputes expressed by the federal and regional professional councils of medicine.
The low rate of participation of nurse-midwives and midwives in childbirth care in Brazil is the result of historical and social construction, which begins with the medicalization of childbirth in the twentieth century, based on Brazilian medical publications that were essential to increase the visibility of the actions of doctors and to convince the lay public about the effectiveness of medicine [35, 36]. With childbirth becoming an increasingly difficult and risky event, specialized medical assistance became indispensable as a way to identify any variation in normality early and correct its defects .
However, more recent studies [38,39,40] show that in order to ensure efficient and effective care in obstetrics it is necessary that nurse-midwives and midwives are part of the staff within a functional health system  which has a qualified health workforce with appropriate skills. This is an important step to ensure that women have access to a quality midwifery service that can provide maternal and newborn health interventions and preventive health care strategies .
The expansion of the participation of nurse-midwives and midwives in labor and childbirth care in Brazilian hospitals therefore depends on a sociological and cultural change, deconstructing the notion that a doctor is the only professional trained to monitor pregnancy and childbirth. In addition, there are structural and organizational barriers to overcome [30, 43]. To have a real impact on care, the WHO recommends that countries should have at least one qualified midwife for every 125 births per year . It is estimated that the Brazilian population will grow by 12%, totaling 222.7 million by 2030. Thus, obstetrics services must attend 4.5 million pregnancies per year by 2030, to guarantee universal access to maternal and child care. Currently, 2049 nurse midwives are registered with the Brazilian Nursing Council . Therefore, the low number of available nurse-midwives is in itself a limiting factor for the expansion of childbirth care by nurse-midwives.
Differences in the organization of childbirth care in Brazilian public and private hospitals may also partially explain the best results observed in childbirth care by nurse-midwives in the public sector [1, 46]. This sector presents organization similar to that of many European countries, with childbirth care provided by a professional linked to the hospital who is paid according to the workload, and not to the production of services . In the private sector, prenatal and childbirth care is usually provided by just one doctor of the woman’s choice . This difference in the organization of public and private services plays a major role in the women’s preference for the type of birth  and influences the childbirth model of care, marked by the insufficient presence of nurse-midwives and midwives .
Finally, in both sectors, the Brazilian model of childbirth care is marked by the overvaluation of technology, a hierarchical system of care, rigid routines, strictly medical responsibility and authority, in addition to the excessive use of clinical interventions and less female protagonism [1, 13, 47, 48]. Such characteristics make it difficult to insert nurse-midwives and midwives in the childbirth scenario, and even more, to respect their autonomy [30, 43].
This study has some limitations. Most of the practices were evaluated based on data from medical records and there is a possibility of differential information bias if the quality of the records varies according to professional category. Not all practices contained in the WHO document have been evaluated due to the lack of available information, which limits the assessment of the care provided. In addition, some practices, such as “monitoring of labor progression” and “Cardiotocography during labor in healthy pregnant women with spontaneous labor” have limitations in their measurement. For the first, we considered the presence of monitoring records of labor progression (digital vaginal examination and auscultation of fetal heart rate), as these records allow assessing the well-being of a woman and her baby. However, we do not have information on the monitoring interval, for example, for cervical dilation, which should be done every 4 h . We also did not identify the partogram model used and whether warning and action lines were used, which is currently not recommended . For these reasons, it is possible that the adequacy of this practice is overestimated. Regarding the variable called “cardiotocography during labor in healthy pregnant women with spontaneous labor”, the main limitation is the lack of information regarding the type of use (whether or not the use is continuous), which may have overestimated inappropriate use. The hospitals included in this study were selected according to a convenience sample, and the results found cannot be extrapolated to the set of hospitals that are part of the PPA. However, the results are consistent with the literature on the subject in national and international publications. Finally, the small number of vaginal births assisted by nurses prevented the assessment of the adequacy of practices during childbirth, thus a gap in knowledge remains.