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Rev. Saúde Pública vol.43 n.3 São Paulo May./Jun. 2009
Factores asociados a tasas de cesárea en hospital universitario
Thiago Mamôru SakaeI; Paulo Fontoura FreitasI, II; Eleonora d'OrsiII
de Pós-Graduação em Ciências Médicas. Universidade
Federal de Santa Catarina (UFSC). Florianópolis, SC, Brasil
IIPrograma de Pós-Graduação em Saúde Pública. Departamento de Saúde Pública. UFSC. Florianópolis, SC, Brasil
To assess factors associated to cesarean section.
METHODS: A cross-sectional study was conducted in a university hospital in Florianópolis, Southern Brazil, from 2001 to 2005. Socioeconomic, reproductive, obstetric and institutional information were collected. Data from 7,249 deliveries was obtained from medical records and admission, delivery and post-delivery records. Cox regression was used in the analysis to estimate cesarean prevalence ratios in the categories of variables studied.
RESULTS: Cesarean rates increased from 27.5% to 36.5% during the period studied and they were higher than those associated with medical indications. After adjustment for confounders cesarean rates were positively associated with previous cesarean section (PR=2.65, 95% CI: 2.31;3.05), non-cephalic presentation (PR=2.23, 95%CI: 1.69;2.95), oxytocin use (PR=1.77, 95%CI: 1.43;2.19), dilatation at admission (PR=2.74, 95%CI: 2.18;3.44), and obstetrician profile (>35% of cesarean sections) (PR=1.82, 95%CI: 1.36;2.42).
CONCLUSIONS: The factors associated with cesarean section indicate the need of interventions focusing on women and their reproductive experience and changes in obstetrician practice as well.
Descriptors: Pregnant Women. Cesarean Section. Risk Factors. Socioeconomic Factors. Prenatal Care. Hospitals, University. Multivariate Analysis.
Analizar factores asociados a la realización del parto cesariano.
MÉTODOS: Estudio transversal realizado en hospital universitario de Florianópolis, Sur de Brasil, de 2001 a 2005. Fueron analizados factores socioeconómicos, de experiencias reproductivas, institucionales y relacionados con la práctica obstétrica. Las informaciones relativas a 7.249 partos fueron obtenidas a partir de prontuarios clínicos y registros de admisión, parto y post-parto. Fue utilizada la regresión de Cox en el análisis para estimar razones de prevalencia de cesárea en las categorías de las variables de interés.
RESULTADOS: Las tasas de cesárea aumentaron de 27,5% a 36,5% en el período y estuvieron encima de aquellas debidas a indicaciones médicas. Posterior al ajuste para confundimento, las tasas de cesárea se mostraron positivamente asociadas con cesárea previa (RP=2,65; IC 95%: 2,31; 3,05), presentación no cefálica (RP=2,23; IC 95%: 1,69; 2,95), uso de ocitocina (RP=1,77; IC 95%: 1,43; 2,19), dilatación al ser admitida (RP=2,74; IC 95%: 2,18; 3,44), y obstetra con tasa de cesárea superior a 35% (RP=1,82; IC 95%: 1,36; 2,42).
CONCLUSIONES: Los factores asociados a mayor probabilidad de cesárea mostraron la importancia de intervenciones direccionadas a la mujer y su experiencia reproductiva, así como cambios en la práctica obstétrica.
Descriptores: Mujeres Embarazadas. Cesárea. Factores de Riesgo. Factores Socioeconómicos. Atención Prenatal. Hospitales Universitarios. Análisis Multivariante.
Brazil has one of the highest rates of cesarean section in the world and has been cited as one of the clearest examples of the abuse of this birth procedure.5,7,20,21 This fact is due to improvements in surgical techniques and pre and post-medical support, which has contributed to an understanding of cesareans as a harmless and over-valued procedure. As a result, the number of medical referrals for this type of birth has increased.
In 1985 the World Health Organization (WHO) indicated that a cesarean rate over 15% is medically unjustifiable.24 However, there has been a global increse in rates, 24 which in Brazil went from 32% in 1994 to 40.2% in 1996. A reduction to 36.9% in the period between 1996 and 1999 was followed by an increase in the rates to 39.9% in 2002.ª
Data from 2002 for Santa Catarina, Southern Brazil, indicated that the state had the eighth highest rate in the country, with 43.8% of births being by cesarean section. In 2004 this figure reached 48.3% in the state and 50% in Florianópolis.ª Even in the maternity section of the university hospital, rates have also been increasing substantially over the last few years (27.5% in 2002 to 36.5% in 2004).b
Those cesareans where there is no medical indication are associated with a higher risk of puerperal infection, maternal mortality and morbidity, premature births, neo-natal mortality and a consequent rise in spending for the health system.22,23
Freitas et al13 suggest that in groups in which better maternal health and lower obstetric risk conditions are to be expected, socioeconomic factors and those relating to age, schooling levels and ethnicity, which are related to the chance of cesarean birth, reflect the abuse of this medical technology in providing delivery assistance, social inequalities in birth outcomes and inverse equity.
A study covering 42 countries reveals the social inequality in the practice of cesarean deliveries, with rates below 1% in the poorest countries.21 In Latin America, even though Brazil has the highest rates, they vary from 41.1% for women who live in urban areas to 16.8% for those living in rural areas.21 Villar et al (2006) corroborate these data in their study in Latin America.22
Identifying the factors that explain the increase in cesarean rates is crucial to find solutions. Studies in Brazil10,c and in other countries3,22 show that those absolutely essential indications, when the life of the mother and/or fetus are at risk, have been overtaken by relative indications.
Several authors point to the current organization of obstetric care as playing an important role in high cesarean rates. The main justifications given by obstetricians are: the convenience for obstetricians of programmed intervention, the uncertainty as to the possibility of hypoxia or fetal trauma and the lack of preparation of the woman for the birth.3,6,17,21
According to some studies, this increase in rates has been due to modifications in doctor and hospital practice during the period, regardless of any medical indication.3,17 Personal factors, relating to the woman and her social environment, as well as regional and institutional factors related to the organization of services, constitute non-medical aspects and are associated with the type of birth in Brazil and with current obstetric practice.5
The objective of this study was to analyze factors associated with cesarean births.
A cross-sectional study was conducted based on data relating to 99.2% of the births that took place in the maternity section of a teaching hospital in the municipality of Florianópolis, Southern Brazil, between 2001 and 2005.
At that time, the university hospital had 30 obstetric beds and 27 obstetricians who were responsible for approximately 1,200 births a year, almost 100 a month. There were no resident obstetricians in the period studied.
The data analyzed were obtained from the protocol of the História Clínica Perinatal Base (HCPB - Perinatal Clinical History Database), stored on the Sistema Informático Perinatal (SIP - Perinatal Informatic System) software that was developed by the Centro Latino Americano de Perinatologia (CLAP - Latin American Center of Perinatology). The information contained on the SIP was supplemented by birth and post-birth data from the patients' clinical and admission records.
The factors investigated as independent variables were categorized into three groups: sociodemographic (mother's age and educational level); reproductive and clinical (previous cesareans, number of children borne, gestational age, number of pre-natal consultations, pathology); relating to the birth, institutional and/or obstetric practice (oxytocin, time of birth, cephalic presentation, profile of the obstetrician).
The inclusion of the obstetrician's profile in one of the categories relating to the cesarean rate was based on the history of the individual average rates of the procedure over the two years prior to the period being analyzed. This variable sought to represent a proxy measure for the degree to which the professionals studied intervened.
From the SIPs, the data were transferred to the SPSS 8.0 program in which the analyses were carried out. Gross and adjusted cesarean prevalence ratios (PRs) were calculated for each of the variables. The choice of the reference category was based on interpretative criteria; the category presenting the lowest risk for cesarean birth was used as the reference.
The adjusted PRs were estimated using Cox regression. The aim was to measure the independent contribution of each of the factors. Other variables defined as potential confounders and/or mediating the outcome were controlled. According to Barros,4 the Cox regression can be used for estimating adjusted prevalence ratios when constant time is considered as equal to 1 and the outcome studied (cesarean yes/no) as the status variable. No standard error correction was carried out because the variables were analyzed categorically, according to the cut-off points of the conceptual model.
The multivariate analysis (Cox regression) was applied to the estimated association between each potential risk factor and the occurrence of cesareans, simultaneously controlled by potential confounders.5
The classic strategies that are applied to the analysis of the association between multiple factors and the outcome consider all variables as belonging to the same level of influence, without distinguishing between confusion and mediation.15
So, variables were included in the model according to a hierarchy based on the theoretical conceptual model (Figure). First, all variables relative to the woman's characteristics (level 1) were included in the model. Then the pre-birth variables (levels 2 and 3) were added at the same time as the variables tested for confounding were assessed as potential mediators of the level 1 maternal characteristics. The same process was applied to the lower level variables, including events that happened during labor (level 4), the obstetrician's profile (level 5) until the outcome of the type of birth was reached.
The study was approved by the Research Ethics Committee of the Universidade Federal de Santa Catarina (protocol 187/2005) and was carried out in accordance with the regulatory guidelines and norms for research involving human beings (Resolution 196/1996 of the Conselho Nacional de Saúde).
Of the 7,249 births in the 2001-2005 period, six were excluded because there was no CLAP registration form. Of the 7,243 births investigated, overall 32.6% were by cesarean section, an increase from 27.5% to 36.5% during the period. In each of the years studied, the rates were higher than those with strictly medical indication for cesareans, according to the WHO.
Table 1 shows the rates and the cesarean PRs for the sociodemographic, reproductive, clinical, institutional and/or obstetric practice variables.
Cesarean rates were highest among women over 30 and those who were primiparous or who were multiparous with a previous cesarean section, when compared with those with previous vaginal birth. Among multipara with prior cesarean section, the probability of them having a cesarean again was more than double than for those who had had one previous cesarean (PR=2.60) and almost five times higher for multipara who had had two or more previous cesareans (PR=4.83). The cesarean rate has proved to be a little higher among women with higher pre-natal consultation frequency (PR=1.16) and those who continued with their education after high school (PR=1.08). The conditions of women at admission and pre-birth that were associated with a higher risk of them having a cesarean were non-cephalic presentation (PR=2.83), non-spontaneous start of labor (PR=2.39), those pregnant with twins (PR=2.24) and dilation less than 3 cm (PR=3.32). Just as influential were the presence of pathology in the pregnancy and/or pre-birth and gestational age less than 37 weeks and over 40 weeks; these factors were also associated with a higher probability that the birth would be by cesarean section, although not to the same extent (PR=1.65 and PR=1.35, respectively). At the level of factors linked to the institution and to obstetric practice, even though the use of oxytocin (PR=1.56) and day shift (PR=1.25) appeared to be associated with higher cesarean rates, the obstetrician's profile (defined by their average rate of cesarean births) was associated with an almost three times higher probability of a cesarean (PR=2.96) when compared to those whose profile was defined as being less interventionist (Table 1).
In the multivariate analysis the influence of factors associated with the occurrence of cesarean births was investigated according to their hierarchical relationship with other factors in the model, as shown in Table 2.
The effects of age, first birth, higher attendance to pre-natal consultations, previous cesarean, non-cephalic presentation, the use of oxytocin, dilation less than 3 cm and the obstetrician's profile remained statistically significant after adjusting for confusion in the multivariate model, as seen in Table 2.
After adjusting for level 1, variables in the hierarchical model the effect of being over 30 remained practically the same and was not mediated to any significant extent by the other variables in the model. At this level the variable most strongly associated with the outcome was a previous cesarean; the risk among women with prior cesarean section was three times higher and for those with two or more previous cesareans, the risk was four times higher. There was a relative drop in the risk of a cesarean among women who had previously had more than one cesarean when admission and pre-birth variables were included in the model, suggesting that the effect was partially mediated by these variables. The mother's schooling level showed risk without statistical significance.
At level 2, a higher pre-natal consultation frequency was also mediated by the same variables, with a loss of effect and statistical significance. At level 3, dilatation less than 3 cm (PR= 2.73) and non-cephalic presentation (PR=2.23) remained significantly associated. However, the effect of "start of labor induced" reduced significantly when the other variables of admission and pre-birth were included in the model, suggesting an intrinsic relationship between these variables.
From level 4, after adjustment, the day shift effect disappeared, while the independent effect of the use of oxytocin remained the same (PR=1.77). However, from this level, the inclusion of institutional and obstetric practice variables (use of oxytocin, shift and obstetrician's profile) did not modify the influence of the higher level variables, showing that these variables were not mediated within the context being studied.
At the final level (5) of influence in the hierarchical model, the interventionist profile of the obstetrician was still associated with the risk of a cesarean being performed, according to the professional's average rates. However, even though the more interventionist profile of the obstetrician remained significant until the end of the model (PR= 1.53 and 1.82, respectively), the effect reduced after adjusting for the reproductive and institutional variables.
Among the social, economic and demographic factors of the woman, her reproductive experience and obstetric practice the most strongly associated with a cesarean birth were previous cesareans, cervical dilation less than 3 cm at admission and non-cephalic presentation. Other independent predictors of a cesarean birth were the use of oxytocin and the obstetrician's cesarean rate.
The study's limitations include the fact that it was carried out in a teaching hospital, with particular characteristics and with patients that have a certain socioeconomic profile; this makes any generalization as far as the general population is concerned questionable. Although the population attending the hospital is not representative of the population of those giving birth in Florianopolis in the period, all social classes are served although there are not so many private patients. Furthermore, the study was carried out using secondary data and is subject to errors of interpretation and/or data entry.
As has already been presented in other studies, several characteristics investigated led to a higher prevalence of cesarean births. The mother's age has been directly related to the prevalence of cesareans.9,11,14 Freitas et al14 (2008) reported that women over 30 have a higher probability of giving birth by cesarean than women under 20. In the present study the mother's age lost effect after the inclusion of the admission characteristics and adverse gestational events' variables, showing that it was mediated by variables lower down in the hierarchical model. Other individual and socioeconomic factors are associated with cesareans, regardless of age and must be considered when the effect of age on the outcome is studied in more depth.
Different studies have reported a greater occurrence of cesarean births among women who have a higher level of education.2,9,14 One of the explanations for this association is the greater affinity and consequently the higher chance for mutual influence between the professional and patient in the higher classes and in the private sector when compared with the public sector.9,14
In this context the relative socioeconomic homogeneity of the patients who attended the university hospital, added to the characteristics of the patient-obstetrician relationship explain the absence in this study of an association between schooling and type of birth. These findings are corroborated by other authors.2,9,12,14
The constitution of a link measured by the number of pre-natal consultations has been seen to be a risk factor for a cesarean birth. Since this association cannot be fully explained by a higher gestational risk of these women, it has been suggested that the type and quality of the information and the suggestions put across by the health service during the pre-natal period may have an influence on the type of birth.1,5,8,9,14 In this study, a positive association between the number of prenatal consultations and the risk of a cesarean birth disappeared after adjusting for the obstetric history and admission characteristic variables, showing the mediating effect caused by these variables in the hierarchical model.
According to the Department of Health and Human Services of the United States in 1978, 98.9% of pregnant women who had had a previous cesarean had a new surgical birth.14 For decades one of the main factors associated with surgical births has been a previous cesarean.9,10,14 In this study the variable most strongly associated with this outcome was a previous cesarean, but with more than three times the risk for women with one previous cesarean and more than four times for those with two or more previous cesareans.
The influence of gestational age on the risk of a cesarean in those who had never given birth before follows a pattern, with lower rates between 36 and 40 weeks and a significant increase after 40 weeks. In a more detailed analysis, cesarean rates are lower between 36 and 40 weeks for patients whose labor starts spontaneously, increasing before 36 weeks or after 39 weeks in women whose labor was induced.16 After adjusting the hierarchical model pre and post-term gestational ages were not associated in a statistically significant way with cesarean births.
Various studies have reported an increased probability of cesarean births among pregnant women with hypertension,23 pre-eclampsia,23 gestational diabetes19,23 and fetus weighing more than 4000 g.19,23
In this study the impossibility of detecting risks related to specific pathologies makes it difficult to interpret the small risk associated with this variable. There is also the possibility of the potential mediating effect of the greater number of pathologies among women with a greater number of pre-natal consultations. This reduces the risk associated with pathologies at the level immediately below in the hierarchical model.
Cervical condition at admission and indication for induction have been reported as having a significant impact on induction success and consequently on the cesarean rate.8,9 D'Orsi et al9 (2003), in their case-control study observed that cervical dilation at the time of admission is still one of the variables most strongly associated with the type of birth. According to these authors, women admitted with less than a 3 cm dilation had an 8.5 times higher chance (CI 95%: 4.3;16.6) of having a cesarean than those admitted with 3 cm or more.
The induction success rate gradually improves according to the increase in cervical dilation. This is reflected in a drop in cesarean rates from 46.9% to 9% for women admitted without any dilation compared with those whose dilation was more than 5 cm.7
Beiswenger et al7 (2002) also pointed out the association between dilation at admission and cesarean rates. The rate among women admitted with the neck of the womb closed was four times higher (32.5% vs. 7.8%) than those whose dilation (p<0.05) was 1 cm or more. This effect continued after adjusting for those patients where a cesarean had been indicated. Cesarean rates also stabilized as dilation increased.7 Just as in various other studies,7,9,14 dilation less than 3 cm was one of the biggest predictors of a cesarean birth.
With regard to handling labor, the association between the use of oxytocin and a smaller chance of having a cesarean was found by Freitas et al14 (1999, 2008) and D'Orsi et al9 (2003). The fact that the risk remains after adjustment suggests that the reduced chance of using oxytocin with women who had a cesarean occurred because probably the decision to have a cesarean had already been taken.9,14
In this study, the use of oxytocin was associated with almost twice the risk of having a cesarean. In an attempt to explain these data better the association between the variables oxytocin and dilation was analyzed. The results (not presented) showed that there was a positive association for dilation less than 4 cm, which reinforces its use for the purpose of inducing and not accelerating the birth.
Some authors report a higher risk of a cesarean being chosen for elective induction in nulliparous women.16,18 Induced labor has been described as having an adverse effect on the health of the mother and the newly-born baby, when compared with spontaneous births, notwithstanding the effect of the epidural analgesic.
In their study of 7,372 nullipara, Hefner et all(2003) showed that 30% had induced births, giving cesarean rates of 24.7%, compared with 13.7% among those where labor had started spontaneously.
D'Orsi et al9 (2003) describe an 80% reduced chance of a cesarean birth in women whose labor started at home, compared with those who started after having been admitted to the hospital.
Some literature has suggested that there is an association between time and type of birth.8,9 D'Orsi et al9 (2003) showed that if the birth happens in the morning or beginning of the afternoon (9:00 a.m. to 2:59 p.m.) the odds of a cesarean was 2.7 times higher (CI 95%: 0.9;8.4) when compared with the early morning period (00:00 a.m. to 5:59 a.m.).
The effect of the obstetrician's profile has been reported as being associated with an increase in cesarean rates. Luthy et al18 (2004) found that adding the variable "obstetrician" to a multivariate model resulted in an adjusted risk that was twice as great for primiparous women with elective cesarean (RR=2.01; CI 95%: 1.57;2.82).
In this study obstetricians with average annual rates located in the intermediary gradient (26% to 35%) had rates that were 50% higher (RR=1.56; CI 95%: 1.16;2.08) when compared with those of obstetricians from the lower gradient. This difference increased to 82% when the same reference category was compared with obstetricians with average annual rates located in the upper gradient.
The strong association between low cervical dilation at the time of admission and the type of birth underline the importance of avoiding early hospital admission, which is wrongly associated with a diagnosis of prolonged labor. The relation between higher pre-natal consultation frequency and cesarean rate in this and other studies indicates the need to reorganize pre-natal services to provide suitable information about the signs of labor.
In our study a previous cesarean increased by up to four times the probability of a new cesarean birth occurring, regardless of the profile of the obstetrician. So preventing cesareans among primiparous women is vitally important, since the cumulative effects of previous cesareans build up over the long term with the consequent higher chance of a new cesarean among these women. Medical training, the use of partograms and accurate information during the pre-natal assistance period can lead to more appropriate pre-natal and obstetric practice conduct.
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Correspondence: Received: 8/14/2007 Article based on
the master´s dissertation by Sakae TM presented to the Programa de Pós-Graduação
em Saúde Pública at Universidade Federal de Santa Catarina in
Paulo Fontoura Freitas
Universidade Federal de Santa Catarina
Programa de Pós Graduação em Saúde Pública
Campus Universitário - Trindade
88040-970 Florianópolis, SC, Brasil
a DATASUS. SINASC- Sistema de Informações de Nascidos Vivos. Ministério da Saúde; 2006 [cited 2006 Feb 27]. Available from: http://www.datasus.gov.br/catalogo/sinasc.htm.
b Data files of the institution.
c Freitas PF. The epidemic of caesarean sections in Brazil, factors influencing type of delivery in Florianópolis, South Brazil. [PhD Thesis]. London: London School of Hygiene and Tropical Medicine; 1999.
Article based on
the master´s dissertation by Sakae TM presented to the Programa de Pós-Graduação
em Saúde Pública at Universidade Federal de Santa Catarina in