Abstract(resumo):

The aim of this study was to assess the trend in cesarean sections in three birth cohorts started in Ribeirão Preto, São Paulo, Brazil, in different years (1978/79, 1994, and 2010), and to investigate sociodemographic and economic factors associated with cesarean delivery in these cohorts. Data were obtainedthe database of the cohorts. Women were interviewed shortly after delivery and information was collectedtheir medical charts. The chi-square test was used to compare the proportion of covariates between modes of delivery. Unadjusted and adjusted Poisson regression models were fit to evaluate the association between cesarean section and the covariates studied in the three cohorts. The level of significance was set at ? < 0.05. There was a trend towards an increase in cesarean delivery in the three cohorts. A greater increase in cesarean sections over the years was observed among women with higher educational levels, older women, and economically advantaged women. In adjusted analysis, variables related to women’s sociodemographic and economic conditions were associated with a higher frequency of cesarean sections in the three cohorts.

Keywords(palavra-chave):

Cohort Study; Cesarean Section; Health Care Disparities; Public Health

Content(conteúdo):

INTRODUCTION

Cesarean section, when properly indicated, is associated with survival of the mother and newborn; however, it should not be seen as an option but rather as a medical indication in cases of birth complications or fetal distress1. The excess number of cesarean sections performed does not justify their clinical use to save the life of the woman and her baby, considering that the global frequency of this type of surgery has doubled in recent decades, accounting for 21% of all births. On the other hand, in some countries, this percentage is about 5%, indicating underutilization of this mode of delivery because of scarce resources. In Brazil, the percentage of cesarean sections reaches 60% and varies across regions of the country, reflecting the use of this mode of delivery based on choices and not on the true needs of the pregnant woman2.
Data from the Brazilian National Health Survey indicate that 45% of pregnant women had a vaginal delivery between 29 July 2017 and 27 July 2019, while cesarean section accounted for 55% of births1. According to the World Health Organization, a cesarean section rate higher than 10% is not related to benefits for the pregnant woman or the baby3. Barros et al.4 found that, although the prevalence of cesarean sections had increased over recent years across all economic classes in the city of Pelotas, 90% of women who gave birth by cesarean section in 2015 were from the richest quintile and 93.9% of cesarean deliveries were performed at private clinics. These rates are difficult to explain based on clinical reasons and are probably associated with elective cesarean section. There are multiple reasons for cesarean delivery, including the absence of pain during labor, greater convenience in scheduling the surgery and a feeling of security due to the use of technologies for this purpose; thus, cesarean sections are more frequent among women who belong to higher socioeconomic classes4.
Historically, birth cohort studies conducted in the city of Ribeirão Preto, São Paulo, Brazil, have revealed important unfavorable outcomes throughout life5-7. Goldani et al.8 demonstrated an increase in the prevalence of obesity among adults born by cesarean section compared to those born by vaginal delivery. Another study addressed the association between hypertension in early adulthood and cesarean section; the risk of developing this condition was increased by 51% in the group born by surgical delivery9.
The Ribeirão Preto cohort studies comprise a period of 32 years and encompass historical changes in Brazilian health care, considering that the 1970s were marked by a transition from home to hospital births in Brazil. These changes were influenced by funding from the National Institute of Social Security (INPS) in 1967, which changed the ways of giving birth in the country from natural births assisted by midwives at home with the partner to medicalized and surgical births10.
Within this context, the aim of the present study was to assess the trend in cesarean sections in three birth cohorts started in Ribeirão Preto in different years (1978/79, 1994, and 2010), and to investigate factors associated with cesarean delivery in these cohorts.

METHODS

This project aims to analyze three birth cohorts (1978/79, 1994, 2010) followed up in the city of Ribeirão Preto, state of São Paulo, Brazil.

1978/79 Cohort
The “Epidemiological-social study of parameters of mother-child health” conducted between 1 June 1978 and 31 May 1979 in Ribeirão Preto, São Paulo, was designed to seek explanations for social inequalities and socioeconomic factors influencing perinatal health, human reproduction, infant mortality, and the utilization of medical services. The study also analyzed some perinatal health indicators and their associations with social and biological variables of the woman and newborn in order to assess the utilization of prenatal health services. Details about the method have been previously published11. Data of the project refer to children born alive in the eight maternity hospitals in Ribeirão Preto, which were obtained by interview with postpartum women and from the records and charts of the maternity hospitals. This cohort was composed of 6,973 live births, including multiple births, corresponding to 98% of all live births to women residing in Ribeirão Preto.

1994 Cohort
In 1994, a new study using a methodology similar to the previous cohort was started. Data were collected from a sample consisting of 1/3 of the births that had occurred in the city that year (all hospital births observed over a period of 4 months). Data on infant mortality in this group were also collected. Interviews were held after delivery and the child’s weight and length were measured immediately after birth. A total of 3,663 births were evaluated, including multiple births. Excluding women who were not residents in the municipality, 2,756 study participants remained12.

2010 Cohort
In 2010, the study called “Etiological factors of preterm birth and consequences of perinatal factors for child health: birth cohorts in two Brazilian cities - BRISA Cohort” (acronym for Brazilian Ribeirão Preto and São Luís Birth Cohort Studies), whose main objective was to investigate new risk factors for preterm birth and their lifelong consequences, was started13. This cohort was conducted at eight public and private hospitals with maternity services from January 1st to December 31st, 2010. All postpartum women from the city were invited to participate in the study and 7,794 live births, including multiple births, were evaluated, corresponding to 96.2% of all births that occurred during the period14. Validated and standardized questionnaires were applied to the postpartum women within the first 24 hours after birth to obtain information on sociodemographic and lifestyle factors, maternal reproductive profile, and childbirth care.

Variables
For the identification of cesarean section in all cohorts, the mode of delivery reported by the women in an interview held after birth was considered. Regarding factors associated with cesarean section, the following covariates shared by all cohorts and obtained by interview with the postpartum women and from the records and charts of the maternity hospitals were analyzed: women’s education level in years of schooling (?12, 9-11, and ?8 years), marital status (with and without partner), women’s age (<20, 20-34, and ?35 years), household income in minimum wages [MW] (<3, 3 to 6, and >6 MW), prenatal care (yes and no) and type of childbirth care (public or health insurance/private car). In addition, newborn weight (<2,500 and ?2,500 g) and gestational age (?39, 37 to 38, 34 to 36, and <34 weeks) were considered.

Data analysis
The data were processed using descriptive and analytical statistics. For this purpose, the absolute and relative frequencies, as well as the 95% confidence interval (95%CI) for proportion, were calculated for the independent and dependent variables. The chi-square test was used to compare the proportion of covariates between modes of delivery. Unadjusted and adjusted Poisson regression models were fit to evaluate the association between cesarean section and the covariates studied in the 1978/79, 1994 and 2010 cohorts. Cases of multiple births (146 in the 1978/79 cohort, 84 in the 1994 cohort, and 188 in the 2010 cohort) and stillbirths were excluded from the analysis. The level of significance was set at ? <0.05 and the analyses were performed using the Stata 14 program (College Station, Texas, USA). In the final model, variables that presented p<0.05 in the unadjusted analysis were added. However, the variable category of childbirth care was not incorporated into the model because it is strongly associated with family income.

Ethical aspects
All procedures of this project were approved by the Research Ethics Committee of the University Hospital of the Ribeirão Preto Medical School, University of São Paulo [FMRP-USP] (Opinion number 5.939.411). The data collection procedures of the 1978/79 and 1994 birth cohorts were not submitted to ethical approval since the Ethics Committee did not formally exist at that time. Consent for holding the interviews was obtained from the Clinical Directors of the hospitals. The objectives of the study were explained to the women. The questionnaires were administered and additional data were obtained from the medical charts of women who gave their consent to participate. The BRISA Cohort was approved by the Research Ethics Committee of the University Hospital of FMRP-USP (Approval number 11157/2008).

RESULTS

1978/1979 Cohort
There were 6,823 data on the mode of delivery, including 69.7% (4,755) for vaginal delivery and 30.3% (2,068) for cesarean section. Although vaginal deliveries predominated in the sample, the data showed that cesarean sections were more frequent among women with higher levels of higher education (45.7%), older women (39.3%), women who lived with a partner (31%), women with higher household incomes (43.5%), and women who received prenatal care (31.7%) and had health insurance or private care for childbirth (48%). Furthermore, cesarean sections were more frequent among infants born at a gestational age ?39 weeks and with a birth weight ?2,500 g (Table 1).

1994 Cohort
In contrast to the findings obtained for the 1978/1979 cohort, vaginal deliveries accounted for 49.2% of births, while cesarean sections accounted for 50.8% of all births performed during the period, totaling 2,756 births. Among women with ?12 years of schooling, 76.9% had a cesarean section, while the highest frequency of vaginal delivery was observed among women with ?8 years of schooling (59.7%).
Among women undergoing cesarean section, the majority were > 35 years old (64.2%), more than half of them had a partner (51.7%) and most of them reported gaining >6 MW (68.4%). Among women delivering by cesarean section, 51.2% received prenatal care, while the percentage of women who did not receive prenatal care was 80.3% among those with vaginal delivery. Health insurance or private care for childbirth predominated among women who underwent cesarean section (77,4%). Furthermore, the frequency of cesarean sections was higher among infants born between 37 and 38 weeks. In this cohort, there was no difference in the frequency of birth weight according to mode of delivery (Table 1).

2010 Cohort
The 2010 Cohort evaluated 7,563 births that had occurred in that year. Cesarean section rates followed the increase seen in the other cohorts, with 58.5% of cesarean sections, while vaginal delivery accounted for 41.5%. As also observed in the other cohorts, cesarean sections continued to be more frequent among more women with higher education levels (85.2%), older women (76.1%), women who lived with a partner (61%), women with higher household incomes (79.5%), women who received prenatal care (59%) and had childbirth care provided by health insurance or private care (90,9%). In this cohort, the cesarean section rate was higher among infants with lower gestational age; however, as in the 1994 cohort, there was no association between the mode of delivery and birth weight (Table 1).
Table 1 shows that the increase in cesarean sections was greater among women with higher levels of education compared to those with lower education (from 45.7%, in 1978/79 to 85.2% in 2010 and from 27.1% in 1978/79 to 36.8% in 2010, respectively). Older women were another group in which the percent increase in cesarean sections was greater over the three cohorts, with an increase of 36.8% between 1978/79 and 2010. Among economically advantaged women, the cesarean section rates increased from 43.5% in 1978/79 to 79.5% in 2010, while the increase was 17.2% over the same period in disadvantaged women. Regarding childbirth care, 91% of women in private hospitals underwent cesarean sections in 2010, compared to 33% in public hospitals. Over the years, there has been a continuous increase in the number of cesarean sections in health insurance/private care, while vaginal births accounted for only 9.1% in this type of healthcare service during the same period.
The results of Poisson regression analyses of the variables studied are shown in Table 2. In the unadjusted model, ?12 years of schooling, living with a partner, women’s age ?35 years, a household income >6 MW, and undergoing prenatal care were associated with cesarean section in the three cohorts.
In the adjusted model, women’s education ?12 years of schooling remained associated with cesarean section in all cohorts, with the strength of the association increasing over time (prevalence ratio [PR] 1.24, 95%CI 1.10; 1.42 in 1978/79; PR 1.43, 95%CI 1.27; 1.61 in 1994, and PR 1.76, 95%CI 1.63; 1.89 in 2010). Women’s age ?35 years was also associated with an increase in cesarean sections in all cohorts, with similar magnitudes across the years (ranging from 1.27 in 1978/79 to 1.20 in 2010), when compared to the reference age (20-34 years). On the other hand, age less than 20 years was found to be a protective factor in all years, with PR ranging from 0.75 in 1978/79 to 0.81 in 2010. Regarding household income, an income >6 MW was associated with cesarean section in all cohorts, with a higher magnitude of PR being observed in 1994 (PR 1.57, 95%CI 1.35; 1.81) when compared to the reference group (<3 MW). In all years, prenatal care was the variable showing the strongest association with cesarean section. This association increased over the years (PR 1.89, 95%CI 1.45; 2.46 in 1978/79; PR 1.97, 95%CI 1.04; 3.71 in 1994, and PR 2.92, 95%CI 1.59; 5.37 in 2010) compared to the group that did not receive prenatal care. The women’s marital status was associated with cesarean section in the adjusted model only in the 2010 cohort, with this surgery being more frequent among women who had a partner (PR 1.18, 95%CI 1.08; 1.29).
Table 3 analyzes the associations between gestational age and birth weight. In the 1978/79 cohort, all gestational ages had a lower occurrence of cesarean sections, considering that in this cohort the majority of surgeries occurred at a gestational age of 39 weeks. In the 1994 cohort, the frequency of cesarean sections was 24% higher for the gestational age of 37 to 38 weeks (PR 1.24, 95%CI 1.15; 1.36), while in the 2010 cohort the frequency of cesarean sections was high in all gestational age categories, up to 38 weeks, including preterm infants. Birth weight <2,500 g was associated with a lower frequency of cesarean sections in the 1978/79 cohort, while no association between this variable and cesarean section was observed in the other cohorts.

DISCUSSION

The present data show a growing trend in cesarean sections in relation to vaginal deliveries in the 1978/79, 1994 and 2010 cohorts conducted in the city of Ribeirão Preto, São Paulo. Furthermore, this increase was more significant among women with higher levels of education, older women, and women with higher incomes, indicating that sociodemographic and economic factors play a role in the choice of the route of delivery in these women.
The cesarean section rate exceeded that of vaginal deliveries from the 1994 cohort onwards; in the 1978/79 cohort, vaginal deliveries were still more common (69.7%) than cesarean sections (30.3%). In the 2010 cohort, 16 years later, cesarean sections accounted for almost 60% of all births. In the study by Barros et al.4 conducted in the city of Pelotas, southern Brazil, cesarean sections increased by 37.3% between 1982 and 2015, accounting for 64.9% of all births in that year. There has been a global increase in the frequency of cesarean sections among women over recent years, particularly in Latin American and Caribbean countries, which is associated with high rates of maternal mortality. Among these countries, Brazil has the second highest cesarean section rate, behind only the Dominican Republic15.
As observed in the present study, there is evidence that socioeconomic factors influence cesarean delivery in different regions of Brazil, disregarding the recommended clinical factors that are essential for performing this surgery. In Pelotas, although the cesarean section rates increased in the four birth cohorts studied (1982, 1993, 2004, and 2015) across all household income quintiles, the richest quintile exceeded the poorest quintile. Furthermore, in 2015, while the number of cesarean sections in the public hospital sector accounted for 51.5% of all births, this percentage was 93.9% in the private sector4.
The percentage of women who underwent cesarean sections in the private sector in 2010 was approximately 91%, with this figure being strongly associated with their income. In line with these findings, the study “Nascer no Brasil”, conducted between 2011 and 2012 with postpartum women, revealed that the incidence of cesarean sections in the public sector was less frequent than in the private sector. Additionally, less educated women had more vaginal births compared to more educated women who gave birth in the private sector16.
Among women with more years of schooling, there was an increase of 39.5% in cesarean section rates from 1978/79 to 2010 when compared to an increase of only 9.7% among those with lower education; in addition, the lowest rate of vaginal deliveries of only 14.8% occurred among women with higher education levels in 2010. Data from the 1996 National Health Survey revealed that 36% of births in Brazil were cesarean deliveries, particularly among women with ?12 years of schooling, with the percentage reaching 81% in this population17. A birth cohort study conducted in São Luís, Maranhão, in 1997/98 also found that the risk of cesarean section was higher among women with higher levels of education18.
In unadjusted analysis, cesarean section rates were higher among women who had a partner. The data indicate a rise in these percentages over the years, with an increase of 30% between 1978/79 and 2010. In the adjusted model, this social variable was associated with cesarean section only in 2010. In the study by Silva et al.18, this percentage was 75% higher among married women of the 1997/98 São Luís birth cohort, thus representing an important social factor for cesarean delivery in northeastern Brazil.
Undergoing prenatal care was associated with an increase of almost 200% in the cesarean section rate in 2010. Despite its paradoxical effect, this fact may be related to the creation of a bond between the woman and her physician, which could increase confidence in accepting suggestions for pre-scheduled deliveries18,19. Furthermore, complications during pregnancy require closer follow-up at the health service, with a consequent increase in the number of prenatal consultations and therapeutic cesarean sections due to a clinical indication. The study by Freitas et al.20 supports the increase in cesarean section rates among women undergoing more prenatal care visits; in addition, the authors highlighted sociodemographic and economic factors such as white skin color and better income conditions to be associated with cesarean delivery.
With respect to gestational age, in the 1978/79 cohort only 13.2% of cesarean births occurred at <34 weeks, while in the 2010 cohort the percentage of preterm births less than this gestational age was 67.6%, demonstrating a considerable increase in the number of preterm births among women who underwent cesarean section. Adjusted analysis showed a lower frequency of cesarean sections for all gestational ages less than 39 weeks in 1978/79, while this percentage was higher for all gestational ages less than 39 weeks in 2010; in 1994, more cesarean sections only occurred at gestational ages between 37 and 38 weeks. This analysis suggests that, with the advances in medical techniques and health technologies, therapeutic cesarean sections may have occurred in 2010, which would explain the numbers of preterm births by cesarean delivery. However, elective cesarean sections without the onset of labor can contribute to the increase in the number of preterm births. Despite the estimation of gestational age, this calculation is inaccurate and can increase the risk of birth of a preterm infant when cesarean section is scheduled to occur before the biological end of pregnancy18,21. Furthermore, preterm birth influences neonatal and maternal health, affecting outcomes throughout the child’s life and increasing hospital costs22. In addition to the impacts on prematurity, cesarean delivery involves a series of other factors that influence the health of the child and its development over time, for example, its impact on colonization of the newborn with intestinal bacteria and the subsequent relationship with the development of obesity in adulthood8,23. Furthermore, the adaptive behavior of children born by cesarean section is compromised, a fact that may influence their psychosocial development throughout life24.
The main limitations of this study are related to memory bias of the postpartum women during application of the questionnaire. To minimize this possible bias, the interviews were held within the first 24 hours after birth by field workers duly trained by the research coordinators at all three time points. The information collected from the medical charts could still be incomplete or contain erroneous data. Furthermore, clinical reasons for cesarean delivery were only considered in the 2010 cohort. It is therefore not possible to compare the three cohorts because of the lack of objective information on the indication for cesarean section in the older cohorts.
In conclusion, in the three study cohorts, there was a significant increase in the number of cesarean sections for pregnancy resolution over the period. This increase was more expressive among women with higher educational levels, older women, and women with higher incomes. These findings suggest that women’s sociodemographic and economic factors influence the execution of cesarean sections and contribute to the increase in this mode of delivery. Women with higher levels of education, older women, and women with higher incomes who live with a partner and who received prenatal care are more likely to undergo this surgery. There is a crucial need for a movement against abusive and elitist practices related to cesarean sections. Health care practices based on scientific evidence must be implemented, combating medical conveniences and misinformation in follow-up consultations.

FINANCIAL SUPPORT

The 1978/79 birth cohort was funded by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the 1994 and 2010 birth cohorts were funded and/or supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Fundação de Apoio ao Ensino, Pesquisa e Assistência do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (FAEPA). The first author received the scientific initiation grant from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).
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