This study estimated the rate of elective (27.8 %) and intrapartum CD (8 %) in primiparous women with a singleton pregnancy and a fetus in the vertex presentation assisted in the public health services in Brazil. The total rate of 35.8 % is high when compared to studies with similar populations. Bryant et al.  found a CD rate of 17.8 % in low risk primiparous in a retrospective cohort study of women delivering at the University of California, San Francisco, between 1980 and 2001 and O’Neill et al  identified a rate of 12.50 % emergency CD and 4.68 % elective, between 1982 and 2010, in a cohort of all live births in primiparous women in Denmark.
Most of the CD in our study was elective but in this analysis, we have identified the factors associated with intrapartum CD. The occurrence of clinical and obstetric conditions potentially related to obstetric emergencies before delivery, a decision in late pregnancy for CD, early admission with < 4 cm of dilatation, and the use of analgesia were associated with a greater proportion of CD. Residing in southeast region, favorable advice for vaginal birth during antenatal care, induction of labor, and the use of any of the good practices during labor were protective factors for CD.
Clinical and obstetric conditions are known risk factors for CD, both elective and intrapartum [18, 19]. We didn’t analyze the CD indications and the management of the clinical and obstetric conditions during antenatal and labor care. Brazil has a high coverture of ANC and in our study, almost all primiparous women had received at least one ANC consultation. However, less than 10 % had an adequate or more than adequate ANC when assessed according to national protocols. Other authors [20, 21] have also pointed out the high rate of inadequacy of ANC in Brazil. This inadequacy can result in adverse outcomes, as many routine practices during ANC are associated with lower rates of maternal mortality and fetal losses . In our study, ANC was not associated with intrapartum CD. This may be the result of residual confounding, as the adequacy score used did not assess the management adequacy of specific conditions.
Antenatal care is not only important for the adequate care of obstetric and clinical complications. Our results show that the receipt of information supportive of a vaginal birth and the decision to choose a vaginal birth at the end of pregnancy were associated with a lower rate of intrapartum CD. Domingues et al.  found that women in the public sector in Brazil are not supported in their choice of vaginal birth, because their preferences for this type of birth diminish during pregnancy. Fear of pain in childbirth is the main reason for women preferring a CD in Brazil and the lack of support during pregnancy may discourage woman, as the birth gets closer.
Induction of labor (IOL) was associated with a lower rate of intrapartum CD. This is a common procedure in different countries and can modify the maternal and perinatal outcomes . The rate of IOL in our study was 17.4 % and is lower than that found by other authors in similar groups: greater than 23 % for all pregnancies with single fetuses in the USA in 2010 ; 29 % in women with 32 or more weeks of gestation in 2007 in Australia . One possible explanation for this smaller induction rate was the high rate of elective CD found in our study. In studies with high- and low-risk pregnancies  or term and post-term pregnancies , IOL was associated with a lower CD rate than expectant management.
Early admission in labor with < 4 cm of dilation is a known risk for CD  and occurred in 37.6 % of women in our sample. Women who are admitted to hospital in the latent phase (<3 cm cervical dilation) have a higher risk of obstetrical interventions, including electronic fetal monitoring, epidural analgesia, oxytocin and CD, than those who are admitted in active labor . Neal et al.  suggested an evidence-based standardized approach for admission for labor to decrease inadvertent admissions of women in pre-active labor: when one cannot diagnose active labor with relative certainty, observation before admission is warranted.
The use of any of the good practices during labor was associated with lower rates of CD. In the Birth in Brazil study, Leal et al.  found a CD rate of 45.5 % and excessive medical interventions during labor and vaginal delivery in low-risk women. Only 3.2 % of low-risk primiparous women had a natural vaginal childbirth and the public health services had the highest rate of use of good practices. The five good practices that were included in the composite adopted in this study—access to fluids or food, freedom to ambulate, use of non-pharmacological methods for pain relief, presence of a companionship, and use of partogram—are part of the recommendations of the Brazilian Ministry of Health  and WHO labor assistance guides .
Restriction of oral intake may be unpleasant for some women, and may adversely influence their experience of labor. In a systematic review of randomized controlled trials and quasi-randomized controlled trials, Singata et al.  concluded that the evidence shows no benefits or harm, and there is no justification for restriction of fluids and food in labor for women at low risk of complications.
Lavender et al.  in a systematic review of randomized and quasi-randomized controlled trials did not find any difference between use of a partogram and no partogram in the risk ratio of CD. However, when comparing the 3- and 4-h action line groups, the CD rate was lowest in the 4-h action line group. Additionally, when a partogram with a latent phase (composite) and one without (modified) were compared, the CD rate was lower in the partogram without a latent phase.
There is evidence that walking and upright positions in the first stage reduces the duration of labor, the risk of CD and the need for epidural. In a systematic review, Lawrence et al found that women who were upright during labor were also less likely to have CD (RR 0.71, 95 % CI 0.54 to 0.94) and less likely to have an epidural (RR 0.81, 95 % CI 0.66 to 0.99) . Leal et al  found that in Brazil less than 50 % of low risk women who went into labor could ambulate. We found similar results in primiparous women.
Almost 10 % of primiparous women in our study had an epidural during labor and its use was associated with an increase in the rate of CD. The effect of epidural analgesia on the CD rate in the literature is controversial. Eriksen et al.  found that the use of epidural analgesia for labor pain was associated with higher risks of emergency CD and vacuum extraction. Other studies did not find any difference in the rate of CD with the use of epidural analgesia, but demonstrated that it is associated with a longer second-stage labor  and increased risk for an instrumental delivery .
The type of professional who provided care during labor was not associated with intrapartum CD in the adjusted analysis. This result is contrary to those observed in studies conducted in different settings [39, 40], including Brazil , and to the results of a systematic review that demonstrated that women who had midwife-led continuity models of care were more likely to experience spontaneous vaginal birth (average RR 1.05, 95 % CI 1.03 to 1.07) .
In our study, the presence of a nurse midwife was associated with increased use of good practices and less use of epidural analgesia, both conditions associated with a lower risk for CD. At a national level, only 18.7 % of primiparous women had access to a nurse midwife whilst being cared for labor. The highest rate was observed in the Southeast, the region that also presented the lowest rate of CD in the country. While future studies are necessary to confirm this hypothesis, it is possible that one explanation for the low rate of CD in the Southeast region is the significantly greater presence of a nurse midwife during labor care in SUS services located in this region. One study conducted in a health service located in this region  demonstrated lower rates of intrapartum CD in labor care provided by a team composed of nurse-midwife and obstetrician working collaboratively when compared to care provided by an obstetrician alone.
Social and demographic factors were not associated with intrapartum CD. Although we didn’t identify age as a risk factor for intrapartum CD, it is noteworthy that almost half of the primiparous women in our study were younger than 20 years. In the USA, in 2012, only 2.5 % of primiparous women were adolescent . In a context of high proportions of young primiparous women, reducing the CD rate is even more important because a uterine scar will have repercussions on the reproductive lives of these young women. Delbaere et al  considered that if physicians want to stop the rising CD rate, they must concentrate on low-risk primiparous women. Reducing primary CD will also have an effect on repeat sections in the future.
This is the first national Brazilian study that has assessed labor and birth care with a sampling process that allows estimates for all macro-regions, location of service (capital and non-capital) and type of service (public, mixed and private). However, this study has some limitations. First, we conducted the study in institutions with more than 500 deliveries each year, which are responsible for almost 80 % of all deliveries . The results presented here are not applicable to smaller hospitals that provide care to less than 500 births/year. Another limitation is the large amount of missing information (48 %) in the variable related to the linkage of the women to the maternity service. However, this occurred because only women who had received guidance provided by ANC on maternity reference for childbirth care answered this question. All other data had at least 89.6 % of information completed. Finally, we had limited information about the use of good practices during labor, as no information was available concerning the duration and time of use of each of the practices assessed. The same limitations apply to the presence of a nurse midwife during labor and the context of her assistance.