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. 2025 Sep 8;20(9):e0319307. doi: 10.1371/journal.pone.0319307

Trends in gestational age at birth in the city of São Paulo, Brazil between 2012 and 2019

Margarida Maria Tenório de Azevedo Lira 1,#, Marina de Freitas 1,#, Eliana de Aquino Bonilha 2,#, Célia Maria Castex Aly 1,#, Patrícia Carla dos Santos 1, Denise Yoshie Niy 3,*,#, Carmen Simone Grilo Diniz 4,#
Editor: Leonardo António Chavane5
PMCID: PMC12416724  PMID: 40920798

Abstract

Studies have shown that excessive obstetric interventions such as induced labor and caesarean sections have contributed to the shortening of the length of gestation, leading to a left shift in gestational age (GA) at birth. The aim of this study was to analyze trends in GA and the contribution of associated factors to changes in São Paulo city, Brazil during the period 2012–2019. We conducted an observational time-series study of births in São Paulo using data from Brazil’s national live births information system (SINASC). We calculated the annual percent change (APC) of births by GA between 2012 and 2019 and between the first and second four-year periods of the time series by applying log transformation to the percentages, followed by Prais-Winsten regression. A total of 1,525,759 live births were analyzed. From 2015, there was an increase in the proportion of live births between 39 and 40 weeks from 2015 and a fall in the proportion of early term (37–38 weeks) and preterm (< 37 weeks) births throughout the study period. The APC of births at 39 and 40 weeks was 7.9% and 5.7%, respectively, while the proportion of births at other gestational ages showed a statistically significant reduction over the study period. These reductions were more pronounced in the first four-year period (2012–2015). The same trend was observed when the data were analyzed by type of delivery, type of service (public or private), maternal age, and maternal education level. The findings show that there was a right shift in the GA curve during the study period and a reduction in the proportion of preterm and early term births. These changes were more pronounced in births that occurred in private hospitals. These changes reflect public policies implemented to reduce obstetric interventions such as induced labor and caesarean section before labor, especially before 39 weeks of gestation.

Introduction

Length of gestation is one of the leading predictors of newborn health outcomes. Gestational age (GA) can be estimated using different methods and is generally measured in completed weeks. Until recently, GA was treated as a binary question, with newborns being considered either preterm (< 37 weeks) or term (37 0/7–41 6/7 weeks), justifying interventions such as labor induction or caesarean section from 37 weeks, when fetal development may not be complete. Studies have shown that the term period should not be treated uniformly, as early term infants (37–38 weeks) tend to have a higher risk of morbidity and mortality than those born between 39 and 41 weeks, often showing similar outcomes to late preterm infants [1–7]. In 2013, the American College of Obstetricians and Gynecologists [8] proposed a different classification of GA, dividing the term period into three categories: early term (37–38 weeks), full term (39–40 weeks), and late term (41 weeks).

The Live Births Information System of Brazil (SINASC) was established in 1996 to systematically collect data on live births across the national territory. Designed to support all levels of Brazil’s healthcare system, SINASC has consistently demonstrated high coverage, completeness, and reliability in its recorded variables. This ensures its capacity to fulfill its primary objective: to provide comprehensive and objective analyses of the healthcare landscape, thereby informing policies that enhance maternal and child health.

In São Paulo, efforts to improve data quality have included rigorous monitoring and continuous professional training for those responsible for completing and inputting information into the Certificate of Live Birth (CLB), SINASC’s foundational reporting form. The training process encompasses the development of educational materials, seminars, and both individual and group workshops. Additionally, healthcare facilities that conduct births and adhere to established standards of completeness and timely data entry receive annual certification through the “SINASC Seal”, reinforcing quality assurance and data integrity [9–11].

SINASC used to record GA as a categorical variable in weekly intervals up to 2010, until the CLB was modified to record this information as a continuous variable. This change enabled a more comprehensive analysis of the distribution of GA. In the city of São Paulo, the new CLB began to be used in 2011, but full implementation across all health facilities only occurred in 2012.

The average physiological length of pregnancy is 280 days, or 40 weeks [12,13]. However, interventions such as scheduled labor induction or caesarean section can shorten the length of gestation [7,14,15]. In Brazil, caesarean section rates have been far higher than the World Health Organization recommended rate of 15% for decades, reaching 57% in the general population [16,17].

In a study investigating the contribution of private sector deliveries in the city of São Paulo to reductions in length of gestation, Diniz et al. [5] found a one-week left shift in GA in infants born by caesarean section through the private health system; the same result was reported by Raspantini et al [18]. A study in Australia [7] investigating trends in the distribution of GA and the contribution of planned births (induced labor and elective caesarean section) to changes also observed a left shift in GA at birth and the findings suggest a changing pattern towards fewer births commencing spontaneously and increasing planned births.

The aim of this study was to analyze trends in GA at birth and the contribution of associated factors in the city of São Paulo during the period 2012–2019.

Materials and methods

Type of study and data source

We conducted an observational time-series study of births that occurred in the city of São Paulo (SP) in the period 2012–2019 using data from the SINASC. The anonymized databases were provided by the São Paulo City Department of Health on May 6, 2020. This study is part of the Potential Pregnancy Days Lost project, which was approved by the Research Ethics Committee of the University of São Paulo’s School of Public Health (CAAE: 98163018.2.0000.5421), on October 11, 2018. Since the analysis used secondary data, individual consent was not required.

Study population and variables

The variables studied were: maternal age and education, mode of delivery, labor induction, type of pregnancy, gestational age, birth weight, type of service, mother’s municipality residence.

We studied liveborn delivered in public and private hospitals at 22–45 weeks of gestation, weighing ≥ 500 grams born to mothers aged between 10 and 49 years. A total of 1,525,759 live births were recorded in SP between 2012 and 2019. Of these, 12,382 (0.8%) were excluded because they did not meet the inclusion criteria (mothers aged under 10 or over 49 years or maternal age not recorded, 272; type of pregnancy not recorded, 40; GA at birth under 22 or over 45 weeks or GA not recorded, 4,388; birth weight < 500 grams or weight not recorded, 922; out-of-hospital births or place of birth not recorded, 6,746; and mode of delivery not recorded, 14), resulting in a final sample of 1,513,377 (99.2%) (Table 1). All variables analyzed in this study showed completeness ranging from 98.9% to 100.0%.

Table 1. Study population and exclusions. City of São Paulo, Brazil, 2012–2019.

Exclusion criteria Exclusions Study population
Total 1,525,759
Mothers aged under 10 and over 49 years or maternal age not recorded 272 1,525,487
Type of pregnancy not recorded 40 1,525,447
GA at birth under 22 or over 45 weeks or GA not recorded 4,388 1,521,059
Birth weight < 500 grams or weight not recorded 922 1,520,137
Out-of-hospital births or place of birth not recorded 6,746 1,513,391
Mode of delivery not recorded 14 1,513,377
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The choice to analyze births occurring in SP stemmed from the need to evaluate the quality and effectiveness of childbirth services within the health system. Given its significance for public health planning, this information is particularly valuable for the health system management of São Paulo city, offering insights that can inform policies and improve maternal care.

The results of the exploratory analysis showed that the GA curves for all live births and singleton births overlapped. These types of pregnancy were therefore analyzed together for the purposes of the present study (Fig 1).

Fig 1. Live births by type of pregnancy.

Fig 1

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City of São Paulo, Brazil, 2012–2019.

Statistical analysis

First, we performed a descriptive statistical analysis of the data, followed by an analysis of trends in GA at birth by calculating the annual percent change of live births over the period 2012–2019. The results showed an increase in the proportion of births between 39 and 40 weeks from 2015. Differences in percent change rates were particularly pronounced between private and public sector births and mode of delivery [19]. A t-test for independent proportions was used to assess whether these differences were statistically significant. We therefore opted to compare the first and last four-year periods (2012–2015 and 2016–2019, respectively) (Fig 2).

Fig 2. Distribution of live births by gestational age.

Fig 2

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City of São Paulo, Brazil, 2012–2019.

Percent change rate was calculated by applying log transformation to the percentages, followed by Prais-Winsten regression [20] to estimate annual percent change (β1) in births by GA. Subsequently, the β₁ values obtained were applied to the following formula to calculate the percent variation rates:

Rate = [−1 + 10β1X 100

The confidence intervals (CI) of the percent change rates were calculated based on the maximum and minimum β values using the following formula:

95%CI=[−1+10βminimum\ X 100; −1+10βmaximum\ x 100]

The null hypothesis (H₀) was that the trend is stationary, i.e., there is no significant difference between the percent change rate and zero, adopting a 95% confidence level. Depending on the percent change rate, the trend may either be increasing (positive value), decreasing (negative value), or stationary, when the null hypothesis is accepted. In the Prais-Winsten regression, the t-test was used to assess the statistical significance of the estimated coefficients. This test evaluates whether each coefficient is significantly different from zero by testing the null hypothesis (H0) against the alternative hypothesis (HA). Data processing and analysis was performed using SPSS version 20 and R.

Results

Table 2 shows that the annual number of live births fell by 8.1% over the study period. The proportion of teenage mothers decreased over the period, while the percentage of mothers aged 35 years and over, mothers with a higher level of education, and multiple pregnancies increased. Deliveries were predominantly caesarean sections, with rates remaining constantly above 50%, although the proportion of this type of delivery fell slightly over the study period. The proportion of pre-labor caesarean sections was high, with rates reaching almost 70% throughout the time series.

Table 2. Annual number of live births and proportions according to maternal sociodemographic and birth characteristics. City of São Paulo, Brazil, 2012–2019.

2012 2013 2014 2015 2016 2017 2018 2019
All Newborn 191,827 191,549 196,780 196,813 187,624 188,574 183,829 176,381
Maternal age (years)
  < 20 12.5 12.4 12.2 11.7 11.2 10.4 9.6 9.0
 20-34 70.5 69.9 69.2 68.9 68.5 67.9 67.5 67.3
 35 and over 17.0 17.7 18.6 19.4 20.4 21.7 22.9 23.7
Maternal education
 Did not complete elementary school 20.7 19.0 17.8 16.7 15.8 14.8 14.0 13.6
 Completed high school 50.6 50.7 50.3 50.5 50.7 50.7 50.7 50.9
 Completed or undergoing higher education 28.6 30.2 31.8 32.7 33.4 34.5 35.3 35.5
Mode of delivery
 Vaginal 42.5 41.2 42.0 43.7 44.0 44.7 45.8 45.5
 Cesarean 57.5 58.8 58.0 56.3 56.0 55.3 54.2 54.5
Labor induction
 Vaginal
  Yes 55.1 55.0 49.1 44.6 39.7 33.9 29.9 27.7
  No 40.3 41.9 48.4 55.2 60.2 66.1 70.1 72.3
  NA/ignored 4.6 3.1 2.5 0.2 0.1 0.0 0.0 0.0
 Cesarean
  Yes 13.9 12.7 12.6 12.5 12.3 11.8 11.8 12.1
  No 83.4 86.0 86.2 87.2 87.5 88.2 88.2 87.9
  NA/ignored 2.7 1.3 1.2 0.2 0.2 0.0 0.0 0.0
CS before labor a
 Yes 68.3 69.9 69.7 67.5 66.7 66.9 67.8 67.5
 No 26.8 27.2 27.5 30.1 30.8 32.4 31.6 32.5
 NA/ignored 4.9 2.9 2.8 2.4 2.5 0.7 0.5 0.1
Type of pregnancy
 Singleton 97.3 97.1 97.1 97.1 97.1 97.0 97.1 97.1
 Multiple 2.7 2.9 2.9 2.9 2.9 3.0 2.9 2.9
Gestational age (weeks)
  < 37 12.1 11.5 10.9 10.4 10.5 10.6 10.5 10.4
 37–38 35.7 36.6 35.9 33.4 31.8 31.5 31.3 31.4
 39–40 43.5 44.5 46.4 50.1 51.5 52.1 52.8 53.0
 41 6.3 5.8 5.6 5.2 5.2 4.9 4.7 4.6
 42 and over 2.4 1.6 1.2 0.9 1.0 0.8 0.8 0.6
Birth weight (g)
  < 2,500 9.6 9.6 9.4 9.4 9.5 9.5 9.5 9.6
 2,500−2,999 24.8 24.9 24.7 24.1 23.9 23.5 23.3 23.5
 3,000-3,999 61.6 61.6 62.0 62.4 62.5 62.7 63.0 62.8
  ≥ 4,000 3.9 3.9 3.9 4.1 4.1 4.3 4.2 4.2
Type of service
 Public 54.6 53.7 54.0 54.4 55.7 56.6 57.4 58.2
 Private 45.4 46.3 46.0 45.6 44.3 43.4 42.6 41.8
Mother’s municipality of residence
 São Paulo 86.6 86.2 85.2 85.5 85.3 85.9 85.9 85.8
 Other 13.4 13.8 14.8 14.5 14.7 14.1 14.1 14.2
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aPercentages calculated only for CS.

Percentages of labor induced births were calculated separately based on total live births for each type of delivery.

The proportion of induced labor vaginal births fell over the period, from 55.0% in 2012 to 27.7% in 2019. With regard to length of gestation, the rate of full-term births (39–40 weeks) increased from 43.5% in 2012 to 53.0% in 2019, while the proportion of births at other gestational ages decreased. The rate of preterm births fell from 12.1% in 2012 to 10.4% in 2015 and remained relatively stable thereafter (Table 2).

Fig 2 shows that the proportion of live births between 30 and 35 weeks remained stable over the study period, while the proportion of births between 36 and 38 weeks fell from 2015, when the percentage of births between 39 and 40 weeks increased.

Fig 3 shows that the most common GA for both spontaneous and induced labor vaginal births was 39 weeks throughout the period. There was an increase in the proportion of spontaneous vaginal births at 39 and 40 weeks over the study period. The proportion of induced labor vaginal births at 39 weeks increased up to 2015, while the proportion of this type of birth at 40 weeks increased over the whole period at a proportionately higher rate than spontaneous vaginal births.

Fig 3. Distribution of spontaneous (a) and induced labor (b) vaginal births by gestational age.

Fig 3

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City of São Paulo, Brazil, 2012–2019.

There was an increase in the proportion of intrapartum caesarean sections at 39 and 40 weeks up to 2015, with rates levelling off in the second four-year period, especially for births at 40 weeks. The most common gestational age for pre-labor caesarean sections was 38 weeks up to 2015, shifting to 39 weeks between 2016 and 2019, with rates remaining above 30% (Fig 4).

Fig 4. Distribution of intrapartum (a) and pre-labor (b) caesarean section births by gestational age.

Fig 4

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City of São Paulo, Brazil, 2012–2019.

There was an increase in the proportion of births at 39 and 40 weeks in public hospitals and normal birth centers over the study period, while in private facilities there was a reduction in the proportion of births at 38 weeks from 2015 and increase in the percentage of births at 39 weeks (Fig 5).

Fig 5. Distribution of live births in public (a) and private (b) hospitals by gestational age.

Fig 5

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City of São Paulo, Brazil, 2012–2019.

The annual percent change increase in the proportion of births at 39 and 40 weeks was 7.9% and 5.7%, respectively, in the period from 2012 to 2019, while the proportion of births at other gestational ages showed a statistically significant reduction over the study period. These reductions were more pronounced in the first four-year period (2012–2015), especially in 36, 37 and 42 weeks and over. There was also a substantial decline in the proportion of births at less than 37 weeks over the study period. This reduction was also more pronounced in the period 2012–2015 (Table 3). The annual percentage change of gestational age of 42 weeks and over was significantly greater than the others in all periods, with an increase during the period from 2012 to 2015 (52.8%) and a decrease during the period from 2016 to 2019 (26.4%).

Table 3. Annual percent change of live births by gestational age. City of São Paulo, Brazil, 2012–2019.

GA 2012–2015 2016–2019 2012–2019
rate (%) 95% CI rate (%) 95% CI rate (%) 95% CI
< 34 −9.2 * (−13.1;-5.1) −2.7 * (−2.7;-2.7) −3.4 * (−6.0;-0.7)
34 −3.4 (−26.3;26.7) −5.4 * (−5.4;-5.4) −4.3 * (−8.4;0.0)
35 −11.1 * (−17.4;-4.3) −2.1 (−11.0;7.7) −5.4 * (−8.9;-1.7)
36 −10.7 * (−15.1;-6.0) 1.6 * (1.6;1.6) −4.7 * (−8.3;-1.0)
37 −10.7 * (−17.6;-3.2) −0.2 * (−0.2;-0.2) −6.2 * (−10.7;-1.5)
38 −2.5 (−11.4;7.2) −2.1 * (−2.8;-1.3) −4.9 * (−7.5;-2.3)
39 12.2 * (6.6;18.1) 2.8 * (2.1;3.6) 7.9 * (4.4;11.5)
40 6.4 * (6.4;6.4) 1.6 * (1.6;1.6) 5.7 * (2.8;8.6)
41 −12.7 * (−14.6;-10.8) −8.4 * (−10.4;-6.3) −9.2 * (−10.7;-7.7)
42 and over −52.8 * (−55.2;-50.3) −26.2 * (−26.2;-26.2) −33.6 * (−43.0;-22.7)
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*p < 0.05 rejects the null hypothesis.

Table 4 shows that there was a positive annual percent change in the proportion of vaginal births at 38–40 weeks over the study period. For births at 37 weeks, the annual percent change over the study period was negative (−7.3%) for caesarean births and positive for vaginal births (+1.2%). In the period 2012–2015, the annual percent change in the proportion of caesarean births at 37 weeks was −12.1%, compared to −6.9% for vaginal births. This difference was statistically significant. The proportion of preterm births decreased across all gestational ages under 37 weeks. This reduction was greater in vaginal births. The decline was significantly greater for 42 weeks and over during the period from 2012 to 2015 for both vaginal and cesarean deliveries (58.7% vs. 46.0%).

Table 4. Annual percent change of live births according to gestational age by type of delivery. City of São Paulo, Brazil, 2012–2019.

2012–2015 2016–2019 2012–2019
Type of birth Vaginal Cesarean t-test Vaginal Cesarean t-test Vaginal Cesarean t-test
GA rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI
< 34 0.2 * (0.2;0.2) −3.2 (−10.0;4.2) −6.5 * (−7.1;-5.8) 0.2 * (0.2;0.2) ** −10.9 * (−14.7;-6.9) 1.9 (−0.9;4.7)
34 −9.8 (−42.3;41.0) 0.5 (−15.1;18.9) −10.3 * (−10.3;-10.3) 0 * (0.0;0.0) ** −9.4 * (−14.7;-3.8) −0.9 (−3.6;1.8) **
35 −14.7 * (−25.8;-1.9) −8.4 * (−12.3;-4.3) ** −8.4 * (−13.6;-2.8) 2.8 (−8.6;15.6) ** −9.0 * (−12.4;-5.5) −2.1 (−6.2;2.3) **
36 −13.9 * (−18.8;-8.7) −6.2 * (−6.2;-6.2) ** −3.4 * (−3.4;-3.4) 5.7 * (5.7;5.7) ** −7.1 * (−10.6;-3.5) −2.9 (−7.1;1.4) **
37 −6.9 * (−7.6;-6.2) −12.1 * (−21.2;-1.9) ** 0.0 * (0.0;0.0) −0.2 * (−0.2;-0.2) ** −3.4 * (−6.0;-0.7) −7.3 * (−12.7;-1.6) **
38 1.4 * (1.4;1.4) −4.1 (−15.3;8.7) ** −0.7 * (−0.7;-0.7) −2.7 * (−2.7;-2.7) ** 1.2 * (0.6;1.7) −7.5 * (−11.0;-3.9) **
39 11.2 * (9.6;12.8) 13.0 * (2.7;24.3) 2.8 * (2.8;2.8) 3.0 * (1.5;4.6) 5.4 * (2.6;8.3) 10.2 * (5.5;15.1) **
40 7.9 * (5.5;10.3) 10.7 * (0.6;21.7) 3.0 * (3.0;3.0) −1.4 (−2.8;0.1) ** 4.2 * (2.5;5.9) 6.4 * (1.3;11.8) **
41 −14.1 * (−14.1;-14.1) −8.8 * (−15.9;-1.1) ** −9.8 * (−15.0;-4.4) −3.8 (−9.3;2.0) ** −12.5 * (−14.4;-10.6) −6.5 * (−8.5;-4.4) **
42+ −58.7 * (−59.9;-57.5) −46.0 * (−48.4;-43.6) ** −28.9 * (−28.9;-28.9) −21.7 * (−30.3;-11.9) ** −37.3 * (−48.2;-24.2) −29.9 * (−38.1;-20.5)
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*p < 0.05 rejects the null hypothesis.

**Statistically significant differences in percent change between vaginal and cesarean births (p < 0.05).

Table 5 shows that there was a positive annual percent change in the proportion of births at 39 and 40 weeks throughout the study period for births in both public and private hospitals. This change was more pronounced in the period 2012–2019 and for births in private facilities. The proportion of births at 37 weeks decreased over the period 2012–2015 in both public and private hospitals (−5.4% versus 14.1%), while the proportion of births at 39 weeks increased (+11.9% versus +13.5%). The findings also show that there was a reduction in the proportion of late preterm births in both public and private hospitals (Table 5).

Table 5. Annual percent change of live births according to gestational age by system (public or private). City of São Paulo, Brazil, 2012–2019.

2012–2015 2016–2019 2012–2019
System Public Private t-test Public Private t-test Public Private t-test
GA rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI rate (%) 95%CI
< 34 −12.7 * (−15.2;-10.1) −4.5 (−10.6;2.0) ** −2.5 * (−2.5;-2.5) −3.4 * (−3.4;-3.4) −4.5 * (−8.6;-0.2) −2.3 * (−3.3;-1.2) **
34 −2.5 (−39.9;58.1) 0 (0.0;0.0) −7.7 * (−7.7;-7.7) −2.3 * (−2.3;-2.3) ** −4.7 (−10.7;1.7) −3.6 * (−5.2;-2.0)
35 −11.7 (−21.5;-0.7) −10.5 * (−12.4;-8.5) −4.1 (−14.0;7.1) 1.4 (−2.3;5.2) ** −5.2 * (−9.2;-0.9) −4.9 * (−9.0;-0.7)
36 −11.1 * (−14.9;-7.1) −7.7 * (−7.7;-7.7) ** 3.0 * (3.0;3.0) 0.2 (−2.7;3.2) ** −3.6 * (−7.7;0.7) −5.6 * (−9.6;-1.4)
37 −5.4 * (−5.4;-5.4) −14.1 * (−24.2;-2.7) ** 2.3 * (2.3;2.3) −2.3 (−5.8;1.4) ** −2.5 (−5.6;0.7) −8.4 * (−13.7;-2.7) **
38 1.2 * (1.2;1.2) −4.9 (−17.3;9.3) ** 0.5 (−1.0;1.9) −4.9 (−9.0;-0.7) ** 0.7 * (0.1;1.2) −7.3 * (−10.8;-3.7) **
39 11.9 * (11.9;11.9) 13.5 * (0.2;28.6) 3.0 * (2.3;3.8) 7.2 (−0.4;15.3) ** 5.4 * (2.6;8.3) 11.7 * (5.8;17.9) **
40 8.1 * (7.4;8.9) 13.2 (−2.9;32.1) 1.2 (−0.3;2.7) −1.8 (−4.0;0.4) ** 4.0 * (1.8;6.3) 6.9 * (0.7;13.5) **
41 −13.3 * (−13.3;-13.3) −1.4 (−20.8;22.9) ** −13.5 * (−13.5;-13.5) −2.7 (−14.7;11.0) ** −12.9 * (−14.3;-11.5) −0.5 (−4.2;3.4) **
42 + −57.0 * (−57.0;-57.0) −35.4 * (−35.4;-35.4) ** −56.3 * (−56.3;-56.3) −21.1 (−25.1;-17.0) ** −36.9 * (−47.3;-24.5) −24.7 * (−30.2;-18.7) **
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*p < 0.05 rejects the null hypothesis.

**Statistically significant differences in percent change between public and private services (p < 0.05).

Tables 6 and 7 shows that there was a significant positive annual percent change in the proportion of births at 39 and 40 weeks across all age groups and levels of education between 2012 and 2019. During these weeks of gestation, higher rates were observed among mothers aged 35 years and over who had completed more than 12 years of education, compared to other categories of educational level and maternal age. Regarding maternal age, a greater decline was noted between 41 and 42 or more weeks of gestation from 2012 to 2015, compared to the period from 2016 to 2019. Additionally, there was a higher increase in gestational weeks 39 and 40 from 2012 to 2015 compared to 2016–2019 (Table 6).

Table 6. Annual percent change of live births according to gestational age by maternal age. City of São Paulo, Brazil, 2012–2019.

2012–2015
Maternal age (years) < 20 20–34 35 and over
GA rate (%) IC95% rate (%) IC95% rate (%) IC95%
< 34 0.2 * (0.2;0.2) −8.4 * (−12.3;-4.3) −15.3 * (−15.3;-15.3)
34 0.5 (−39.0;65.4) −4.5 (−24.5;20.7) −3.4 (−27.9;29.5)
35 −11.1 * (−18.0;-3.6) −10.3 * (−18.4;-1.3) −15.7 * (−15.7;-15.7)
36 −7.7 * (−11.7;-3.6) −9.2 * (−9.2;-9.2) −11.5 * (−17.7;-4.8)
37 −7.3 * (−10.7;-3.9) −11.5 * (−18.3;-4.1) −11.9 * (−19.3;-3.8)
38 −0.2 (−3.1;2.7) −4.3 (−13.0;5.3) −0.2 (−13.2;14.7)
39 11.9 * (11.9;11.9) 12.5 * (7.6;17.5) 13.0 * (2.0;25.2)
40 9.4 * (7.0;11.8) 7.9 * (7.9;7.9) 10.2 (−3.5;25.7)
41 −15.3 * (−15.3;-15.3) −11.3 * (−12.6;-10.0) −9.0 (−16.7;-0.6)
42 and over −55.6 * (−62.8;-47.1) −52.0 * (−55.1;-4.8) −50.0 * (−62.4;-33.5)
2016–2019
Maternal age (years) < 20 20–34 35 and over
GA rate (%) IC95% rate (%) IC95% rate (%) IC95%
< 34 −1.6 (−7.9;5.1) −4.9 * (−4.9;-4.9) 0.2 * (0.2;0.2)
34 0.0 * (0.0;0.0) −8.6 * (−11.9;-5.2) 0 * (0.0;0.0)
35 −7.5 * (−7.5;-7.5) −2.5 (−11.4;7.2) −1.1 (−14.6;14.5)
36 −6.0 (−11.4;0.0) 0.9 * (0.9;0.9) 5.0 (0.0;9.7)
37 −5.2 * (−5.2;-5.2) −1.1 * (−1.1;-1.1) −0.7 * (−0.7;-0.7)
38 −0.5 (−5.4;4.8) −3.4 * (−4.1;-2.7) −2.1 * (−2.1;-2.1)
39 6.4 * (6.4;6.4) 3.5 * (2.8;4.3) 0.5 * (0.5;0.5)
40 1.6 * (1.6;1.6) 2.6 * (1.8;3.3) 3.5 * (1.3;5.8)
41 −5.4 * (−6.8;-4.0) −8.2 * (−8.2;-8.2) −7.1 * (−7.1;-7.1)
42 and over −27.4 * (−27.4;-27.4) −23.6 * (−23.6;-23.6) −27.9 * (−37.3;-17.1)
2012–2019
Maternal age (years) < 20 20–34 35 and over
GA rate (%) IC95% rate (%) IC95% rate (%) IC95%
< 34 −4.5 * (−8.6;-0.2) −3.6 * (−5.7;-1.5) −2.3 (−5.9;1.5)
34 −5.8 (−13.2;2.2) −5.2 * (−8.2;-2.0) −3.2 (−8.8;2.8)
35 −7.3 * (−9.3;-5.3) −5.2 * (−8.7;-1.5) −5.4 (−10.4;-0.0)
36 −4.7 * (−6.8;-2.6) −5.8 * (−9.3;-2.2) −4.7 (−9.8;0.6)
37 −5.4 * (−6.4;-4.3) −7.3 * (−11.7;-2.7) −6.9 * (−11.8;-1.7)
38 0.7 (−0.4;1.8) −6.2 * (−8.8;-3.7) −5.6 * (−9.1;-1.9)
39 5.4 * (3.2;7.8) 8.1 * (5.2;11.1) 9.1 * (3.9;14.6)
40 4.5 * (1.7;7.4) 7.2 * (4.3;10.1) 7.9 * (4.4;11.5)
41 −12.3 * (−15.1;-9.4) −7.5 * (−9.0;-6.0) −5.2 * (−7.7;-2.5)
42 and over −35.9 * (−45.2;-24.9) −32.1 * (−42.3;-20.0) −32.5 * (−40.8;-23.1)
Open in a new tab

*p < 0.05 rejects the null hypothesis.

Table 7. Annual percent change of live births according to gestational age by education level. City of São Paulo. 2012–2019.

2012–2015
Education Did not complete elementary school/ Did not complete elementary school Completed high school Completed or undergoing higher education
GA rate (%) IC95% rate (%) IC95% rate (%) IC95%
< 34 0.2 * (0.2;0.2) 0.2 * (0.2;0.2) −2.5 (−12.7;8.8)
34 −3.2 (−45.3;71.5) −2.7 (−26.4;28.5) 0 (0.0;0.0)
35 −13.9 * (−15.2;-12.6) −9.8 (−21.6;3.6) −11.7 * (−13.6;-9.7)
36 −12.9 * (−16.7;-9.0) −8.2 * (−8.2;-8.2) −8.0 * (−8.0;-8.0)
37 −5.8 * (−9.2;-2.3) −10.1 * (−16.4;-3.2) −16.1 * (−23.1;-8.3)
38 0.9 * (0.9;0.9) −2.7 (−8.3;3.1) −7.7 (−20.3;6.8)
39 0.5 * (0.5;0.5) 11.9 * (8.7;15.3) 13.5 (0.2;28.6)
40 0.5 * (0.5;0.5) 8.4 * (8.4;8.4) 21.6 * (5.0;40.8)
41 0.2 * (0.2;0.2) −12.3 * (−12.3;-12.3) 4.5 * (4.5;4.5)
42 and over −55.3 * (−55.3;-55.3) −52.4 * (−54.4;-50.2) −33.8 * (−47,6;-16.3)
2016 a 2019
Education Did not complete elementary school/ Did not complete elementary school Completed high school Completed or undergoing higher education
GA rate (%) IC95% rate (%) IC95% rate (%) IC95%
< 34 0 (0.0;0.0) −2.5 (−4.6;-0.3) −3.2 (−8.7;2.7)
34 −1.8 (−17.7;17.1) −6.7 (−13.3;0.4) 0 (0.0;0.0)
35 −0.2 (−12.6;13.8) −2.3 (−8.5;4,4) −1.8 (−12.0;9.6)
36 6.9 * (6.9;6.9) −1.4 * (−2.1;-0,6) 3.0 * (3.0;3.0)
37 3.0 (−3.5;10.1) −1.4 * (−1.4;-1.4) −0.2 * (−0.2;-0.2)
38 0.5 * (0.5;0.5) −2.1 (−4.2;0.1) −4.3 * (−4.3;-4.3)
39 4.2 * (4.2;4.2) 3.3 * (2.5;4.0) 2.1 * (2.1;2.1)
40 −0.5 * (−0.5;-0.5) 2.8 * (2.8;2.8) 4.0 * (3.2;4.8)
41 −16.4 * (−17.0;-15.8) −9.4 * (−9.4;-9.4) 5.9 (−0.1;12.3)
42 and over −29.0 * (−29.0;-29.0) −26.9 * (−26.9;-26.9) −15.1 * (−15.1;-15.1)
2012–2019
Education Did not complete elementary school/ Did not complete elementary school Completed high school Completed or undergoing higher education
GA rate (%) IC95% rate (%) IC95% rate (%) IC95%
< 34 −3.8 (−8.9;1.5) −3.4 (−7.0;0.4) −1.8 (−3.9;0.3)
34 −6.0 (−13.4;2.0) −3.8 (−7.9;0.4) −3.8 * (−5.4;-2.3)
35 −3.6 (−9.2;2,3) −4.1 * (−7.6;-0.3) −6.9 * (−10.4;-3.3)
36 −2.7 (−7.9;2.7) −4.9 * (−8.5;-1.2) −6.0 * (−10.0;-1.8)
37 −2.3 (−5.9;1.5) −6.0 * (−9.5;-2.4) −9.6 * (−15.4;-3.5)
38 0.7 * (0.7;0.7) −4.7 * (−6.3;-3.2) −9.4 * (−13.3;-5.4)
39 5.7 * (2.8;8.6) 7.2 * (4.3;10.1) 10.4 * (4.6;16.6)
40 4.0 * (0.1;8.0) 5.7 * (3.4;8.0) 14.3 * (7,1;22,0)
41 −14.1 * (−15.0;-13.2) −9.6 * (−11.1;-8.1) 9.6 * (5.5;13.9)
42 and over −36.9 * (−46.1;-26.1) −33.3 * (−42.7;-22.3) −18.5 * (−26.1;-10.1)
Open in a new tab

*p < 0.05 rejects the null hypothesis.

In weeks 39 and 40, there was a greater decline in the annual percent change during the period from 2012 to 2015 compared to the period from 2016 to 2019 and levels of education. Additionally, APC declined more sharply in gestational weeks 41 and 42 and over, across all maternal education levels and study periods (Table 7).

Discussion

Our findings show that there was a decrease in the proportion of preterm (< 37 weeks) and early term (37–38 weeks) births between 2012 and 2019 and an increase in the proportion of births at 39 and 40 weeks from 2015. The caesarean section rate declined over the study period. However, this method remained the most common mode of delivery, with rates being higher in private hospitals. The increase in the proportion of births at 39 and 40 weeks was higher for births by caesarean section.

The results also show that there was a reduction in the proportion of labor induced births over the study period. This may be partially explained by the modification to the CLB in 2011. Data quality has improved over time, especially in the city of São Paulo, where health professionals have received training on how to complete the form and the importance of differentiating between induced and natural labor [21].

International studies have reported a left shift in GA at birth [1,7] and increase in rates of late preterm and early term births related to a rise in obstetric interventions. Caesarean section rates vary widely across countries. However, countries with optimal maternal and neonatal indicators tend to have lower c-section rates, such as Finland (16.0%), Norway (16.1%), the Netherlands (17.3%) and Sweden (17.4%) [22].

Studies in Brazil [6,16,23], including São Paulo [5,18], have shown that scheduled caesarean sections, particularly in private hospitals, and induced labor early term births have contributed to shortening the length of gestation and a left shift in GA at birth. In contrast, the present study observed a right shift in the GA curve from 2015, with an increase in the proportion of births at 39 and 40 weeks and reduction in preterm and early term births. Our results also show that these changes were more pronounced for births in private hospitals. This trend may be partially attributed to a decline in obstetric interventions – such as labor induction and elective caesarean sections – particularly before 39 weeks of gestation. It is worth highlighting that the rate of increase in the proportion of births at 39 weeks was higher than the rate of fall in caesarean sections between 2012 and 2019. The APC of gestational ages ≥42 weeks declined more sharply after the 2012 recommendation to terminate pregnancies upon reaching 41 completed weeks [24].

It is reasonable to assume that factors other than the implementation of women’s health policies in the 1980s may have influenced the findings of the present study. In 2006, the women’s organization Rede Parto do Princípio reported the abuse of caesarean delivery in the private health system to the Public Prosecutor’s Office (MPF, acronym in Portuguese) [25,26]. The MPF accepted the complaint and filed a public interest civil lawsuit seeking to force the private health sector regulator, the Agência Nacional de Saúde Suplementar (ANS), to regulate the quality of obstetric services provided by the private health system [27], where caesarean section rates are particularly high, reaching 100% in some maternity units. On 6 January 2015, the ANS issued Normative Resolution 368 [28], which sets out measures to ensure that private health insurance policy-holders have access to data on caesarean section rates by healthcare operator and health facility and making the use of partographs and maternity notes mandatory. In March 2015, the ANS also launched the “Adequate Birth Project” [26] which promotes a set of strategies aimed at improving childbirth support to reduce caesarean section rates. In March 2016, the Federal Medical Council issued Resolution 2144 recommending that elective caesarean sections should only be performed from 39 weeks of gestation to guarantee the safety of the baby [29].

The combination of these factors helped draw attention to the excessive use of the caesarean section in the private sector, empowering women to make informed birth choices. Our findings show that 2015 was an inflection point for caesarean section rates in SP, with an increase in the proportion of this type of birth at 39 weeks up to the end of the time series. This rise was more pronounced in private sector births.

Early caesarean sections without a medical reason can have adverse effects on short- and long-term maternal and infant health and well-being. At the end of pregnancy, every day counts and the more the birth is brought forward the higher the risk of infant mortality [30]. Thus, monitoring trends in GA at birth can help assess not only chances of survival but also future health. The reduction in preterm and early term births and increase in the proportion of births at later GAs is therefore good news. Nevertheless, induced labor and caesarean births remain the most common mode of delivery in SP, showing that non-evidenced based practices prevail in the country’s most populous city.

Limitations

This study has inherent limitations associated with the use of secondary databases. While these sources are characterized by high quality and reliability, they do not allow for an in-depth exploration of childbirth humanization or an assessment of maternal satisfaction with the care received. Nonetheless, the findings—particularly the observed reduction in preterm and early-term births among cesarean deliveries—indicate that policies aimed at improving maternal and postpartum care have already yielded positive outcomes, underscoring the importance of their continuation and refinement.

Additionally, the scope of social variables analyzed was limited to maternal education and age. Future research could expand this framework by incorporating other relevant factors, such as the mother’s residential neighborhood and racial background, to provide a more comprehensive understanding of childbirth care disparities.

Recommendations

There is still a long way to go to improve intrapartum care in Brazil, which entails the uptake of national and international recommendations [31–33], including:

  • (1)

    the use of evidence-based practices, promoting a change in culture, where childbirth is not seen primarily as a high-tech medical event.

  • (2)

    the dissemination of an antenatal intrapartum care model involving interdisciplinary teams, including autonomous obstetric nurses and midwives for low-risk pregnancies and the active participation of women in their childbirth [34].

  • (3)

    the strengthening of the country’s public health system, the Sistema Único de Saúde (SUS) or Unified Health System, and its principles and guidelines, including public participation and the dissemination of information on women’s rights.

  • (4)

    the transparent monitoring of data and service and professional performance indicators.

  • (5)

    the regulation of intrapartum care practices and price setting in the private sector to ensure good ethical standards.

It is hoped that the effective implementation of these recommendations will make birth safer and improve women’s satisfaction with the childbirth experience, positively influencing long-term infant outcomes. This constitutes a broad health care agenda that merits priority attention if we want to promote the health of women and the next generations.

Acknowledgments

This study is part of the “Potential pregnancy days lost” (PPDL) project, which provides an innovative measure of gestational age to assess maternal and child health interventions and outcomes. The project was developed in partnership with the São Paulo City Department of Health, Bill & Melinda Gates Foundation (reference number INV-027961), and National Council for Scientific and Technological Development (CNPq/DECIT-MS reference number 445116/2020–0).

Data Availability

The database is fully available for consultation at the Harvard Dataverse Repository: https://doi.org/10.7910/DVN/PP2VVF.

Funding Statement

The project was developed in partnership with the São Paulo City Department of Health, Bill & Melinda Gates Foundation (reference number OPP1201939 - https://www.gatesfoundation.org/), and National Council for Scientific and Technological Development (reference number 443775/2018 – Fundação Bill e Melinda Gates/CNPq/DECIT-MS - https://www.gov.br/cnpq/pt-br). CSGD is a Research Productivity Fellow - Level 2 from the National Council for Scientific and Technological Development. MMTAL received a Industrial Technological Development Scholarship - Level B from the National Council for Scientific and Technological Development. MF received a Industrial Technological Development Scholarship - Level B from the National Council for Scientific and Technological Development. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Decision Letter 0

André Ricardo Ribas Freitas

14 Mar 2025

PONE-D-25-03233Trends in gestational age at birth in the city of São Paulo, Brazil between 2012 and 2019PLOS ONE

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4. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: No

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Type of study and data source

It would be interesting to put the website address from which the data was downloaded (line 81).

I think the study is an observational follow-up study and not an ecological one.

Study population

In lines 86 and 87 the authors say: “Births without information on type of delivery, GA, and type of pregnancy were excluded (Table 1)”. Did all live births in SP between 2012 and 2019 have their gestacional age and birth weight recorded?

In the version of the article I had access to,I coudn´t find Figure 1 that the authors mention in line 98. On line 100 there is only the title of the figure: “Figure 1. Live births by type of pregnancy. City of São Paulo, Brazil, 2012-2019. ” Please check.

Statistical analysis

In lines 110, 111 and 112 the text is in Portuguese. Please check.

Results

In Table 2, the decimal separator for the percentages has a comma, but the manuscript is in English. Please check.

The sum of the percentages of maternal age and education (Table 2) does not add up to 100%. Please check. Why don´t the percentages of Labor induction and CS before labor add up to 100%?

Again, I don´t have any of the figures mentioned in the article, so I couldn´t follow the comments the authors make between lines 139 and 167.

In Table 3, the decimal separator for the percentages has a comma, but the manuscript is in English. Please check.

In Table 3 I suggest that instead of rate the authors use APC (average annual change) in percent. The title of the table reads “Average anual percent change in proportion”. Percent in proportion, what does that mean?

In Tables 4 and 5 keepthe format of the presentation of the columns as in Table 3, ie, first the columns 2012 to 2015, then 2016 to 2019 and the last columns for 2012 to 2019. Was the t-test that the authors show obtained from the regression model or were there seral t-tests comparing the APC’s? In the methodology, the authors make no mention of this test and don´t even say anything about the level os sigificance adopted in the work.

In Table 6, the authors didn´t analyze the two periods as they did in the other tables, why?

In Tables 4 to 6 the APC for GA 42 and over are very high when compared to the other GA’s, but the authors make no comment on this. Why?

References

Reference 19 is missing the year of publication.

Rêgo M, Leão DC, Luiza M, Riesco G, Schneck CA, Angelo M. Reflexões sobre o excesso de cesarianas no Brasil e a autonomia das mulheres Reflections on the excessive rates of cesareans in Brazil and the empowerment of women. : 2395–2400.

In reference 24, the final part of the article´s title is missing

Queiroz MR, Junqueira MER, Lay AAR, Bonilha EDA, Borba MF, Aly CMC, et al. Neonatal mortality by gestational age in days in infants born at term : A cohort study in Sao. PLoS ONE. 2022;17: 1–11. doi:10.1371/journal.pone.0277833

Reviewer #2: The aim of this study was to analyze trends in GA at birth and the contribution of associated factors in the city of São Paulo during the period 2012-2019, through an ecological time-series study, using data from Brazil’s national live births information system (SINASC). The topic is relevant to Public Health. However, the manuscript needs a set of adjustments.

Introduction

- I suggest inserting the paragraph about SINASC (lines 59 to 63) in the Materials and Methods section.

Materials and Methods section

- the objective of the study is to analyze the trends in Gestational Age at birth in the city of São Paulo. However, when considering births that occurred in the city of São Paulo, the total number of live births in the city of São Paulo is obtained, regardless of the mother’s place of residence. How can this fact affect the results and conclusions of the study? Therefore, I suggest two possibilities: to present the answer to this question in the limitations of the Discussion section, or to redo the analyses considering only live births of mothers residing in the city of São Paulo who gave birth in the city itself.

- In Table 1, correct the excluded values of the variables “Gestational Age”, “birth weight” and “out of hospital births”, adding the values without information.

- I suggest adding a topic to describe the variables used in the study.

- Why was the variable “race/skin color of the mother”, available in SINASC, not included in the Prais-Winsten regression analysis? I suggest justifying or adding this variable.

- I suggest standardizing the use of the term “Annual Percent Change (APC)” instead of “Percent change rate” in the Statistical analysis section.

- In lines 110-112, translate the sentence into English.

- Correct the formula in line 113, replacing “e” with “10”.

- Cite the version of the SPSS software.

- Cite and justify the application of the “t-test” in tables 3 and 4. Why was this statistical test not presented in table 6?

- Since ensuring quality information is an essential condition for the analysis of epidemiological indicators (proportions), I suggest calculating the completeness of the variables used in the study, in the period 2012-2019.

Results

- In tables 3, 4, 5, 6, I suggest "APC" instead of "rate" and adding the respective p values.

- In lines 172-173, the authors report that “These reductions were more pronounced in the first four-year period (2012-2015)”. I suggest applying a statistical test to identify differences between the periods 2012-2015” and “2016-2019”.

- In line 183, correct the APC value “for vaginal births”.

- In lines 208-209, the authors report that “Rates were higher among mothers aged 35 years and over and who had completed more than 12 years of education”. I suggest applying a statistical test to identify differences between age groups and educational levels.

- Why in Table 6 were the same analyses not performed for the periods “2012-2015” and “2016-2019”? I suggest standardization according to the results presented in Tables 3, 4 and 5.

- For Figures 2, 3, 4 and 5, I suggest applying a statistical test to identify differences in the proportions of the variables during the study period.

Discussion

- The discussion section could be more in-depth, citing other studies with similar designs (ecological time-series study) that evaluated the same outcome (trends in GA at birth) in Brazil and other countries.

- Included the limitations of ecological studies and other limitations of the analysis of Health Information Systems.

I suggest including a paragraph in the discussion addressing how social inequalities in the city of São Paulo and the COVID-19 pandemic can affect the conclusions of the study.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy .

Reviewer #1: No

Reviewer #2: No

**********

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Attachment

Submitted filename: Comments.docx

pone.0319307.s001.docx (13.5KB, docx)
PLoS One. 2025 Sep 8;20(9):e0319307. doi: 10.1371/journal.pone.0319307.r002

Author response to Decision Letter 1

12 May 2025

Dear Editor,

We are thankful for the thorough review of our manuscript. We have made our best to meet the reviewers’ suggestions, as described below.

Journal Requirements:

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming.

We did our best to meet the journal's style requirements.

2. Please include your full ethics statement in the ‘Methods’ section of your manuscript file. In your statement, please include the full name of the IRB or ethics committee who approved or waived your study, as well as whether or not you obtained informed written or verbal consent. If consent was waived for your study, please include this information in your statement as well.

We included the requested information in the Methods section, as follows:

“This study is part of the Potential Pregnancy Days Lost project, which was approved by the Research Ethics Committee of the University of São Paulo's School of Public Health (CAAE: 98163018.2.0000.5421), on October 11, 2018. Since the analysis used secondary data, individual consent was not required.”

3. We note that you have included the phrase “data not shown” in your manuscript. Unfortunately, this does not meet our data sharing requirements. PLOS does not permit references to inaccessible data. We require that authors provide all relevant data within the paper, Supporting Information files, or in an acceptable, public repository.

All data can be accessed in Harvard Dataverse, and we included a reference for that (https://dataverse.harvard.edu/dataverse/DPGP).

4. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references.

We reviewed the reference list and to the best of our knowledge no cited paper has been retracted. We added some references, as required and explained below.

Reviewer #1:

Type of study and data source

1. It would be interesting to put the website address from which the data was downloaded (line 81).

The databases were provided by the Health Department via ftp link. To clarify that, we included the following information:

“The anonymized databases were provided by the Sao Paulo Municipal Health Department on May 6, 2020.”

2. I think the study is an observational follow-up study and not an ecological one.

We changed the description to "observational time-series study", as required.

Study population

3. In lines 86 and 87 the authors say: “Births without information on type of delivery, GA, and type of pregnancy were excluded (Table 1)”. Did all live births in SP between 2012 and 2019 have their gestational age and birth weight recorded?

No. The proportion of unavailable information for gestational age ranged from 0.01% to 1.20%, with an average of 0.25% (2012-2019). For birth weight, the proportion of unavailable data varied between 0.001% and 0.007%, with an average of 0.003% during the period.

We excluded all live births that did not have one or more of the following information: maternal age, type of pregnancy, gestational age, birth weight, place of birth or type of delivery. We modified the above mentioned paragraph to clarify that, and included the following information:

4. In the version of the article I had access to,I couldn't find Figure 1 that the authors mention in line 98. On line 100 there is only the title of the figure: “Figure 1. Live births by type of pregnancy. City of São Paulo, Brazil, 2012-2019. ” Please check.

We apologize for that - we uploaded all the figures again, following the journal's requirements. Additionally, we uploaded a pdf version with all figures.

Statistical analysis

5. In lines 110, 111 and 112 the text is in Portuguese. Please check.

We apologize for that. The text was translated to English.

Results

6. In Table 2, the decimal separator for the percentages has a comma, but the manuscript is in English. Please check.

We checked all the tables so that all values have a dot as a decimal separator.

7. The sum of the percentages of maternal age and education (Table 2) does not add up to 100%. Please check. Why don't the percentages of Labor induction and CS before labor add up to 100%?

We revised the table to clarify how the calculations were performed and we presented all the values related to the mentioned variables.

8. Again, I don't have any of the figures mentioned in the article, so I couldn´t follow the comments the authors make between lines 139 and 167.

We apologize for that - we uploaded all the figures, following the journal's requirements.

9. In Table 3, the decimal separator for the percentages has a comma, but the manuscript is in English. Please check.

We checked all the tables so that all values have a dot as a decimal separator.

10. In Table 3 I suggest that instead of rate the authors use APC (average annual change) in percent. The title of the table reads “Average annual percent change in proportion”. Percent in proportion, what does that mean?

We changed the text and the table's title, as requested.

11. In Tables 4 and 5 keep the format of the presentation of the columns as in Table 3, ie, first the columns 2012 to 2015, then 2016 to 2019 and the last columns for 2012 to 2019.

We reworked the tables, as requested.

12. Was the t-test that the authors show obtained from the regression model or were there seral t-tests comparing the APC’s? In the methodology, the authors make no mention of this test and don't even say anything about the level of significance adopted in the work.

The test had been done. We updated the methods section to include this information, as requested.

13. In Table 6, the authors did not analyze the two periods as they did in the other tables, why?

We reworked the table, as suggested.

14. In Tables 4 to 6 the APC for GA 42 and over are very high when compared to the other GA’s, but the authors make no comment on this. Why?

We added comments about this finding in the Results section.

The APC of gestational ages ≥42 weeks declined more sharply after the 2012 recommendation to terminate pregnancies upon reaching 41 completed weeks (reference included: Gülmezoglu, A. Metin, et al. "Induction of labour for improving birth outcomes for women at or beyond term." Cochrane database of systematic reviews 6 (2012).

References

15. Reference 19 is missing the year of publication.

We included the year of publication.

16. In reference 24, the final part of the article’s title is missing.

We included the missing information.

Queiroz MR, Ramos Junqueira ME, Roman Lay AA, Bonilha EA, Borba MF, Castex Aly CM, Moreira RA, Diniz CSG. Neonatal mortality by gestational age in days in infants born at term: A cohort study in Sao Paulo city, Brazil. PLoS One. 2022 Nov 21;17(11):e0277833. doi: 10.1371/journal.pone.0277833. PMID: 36409732; PMCID: PMC9678289.

Reviewer #2:

1. I suggest inserting the paragraph about SINASC (lines 59 to 63) in the Materials and Methods section.

We added it in the Methods section: The Live Births Information System of Brazil (SINASC) was established in 1996 to systematically collect data on live births across the national territory. Designed to support all levels of Brazil’s healthcare system, SINASC has consistently demonstrated high coverage, completeness, and reliability in its recorded variables. This ensures its capacity to fulfill its primary objective: to provide comprehensive and objective analyses of the healthcare landscape, thereby informing policies that enhance maternal and child health.

In São Paulo, efforts to improve data quality have included rigorous monitoring and continuous professional training for those responsible for completing and inputting information into the Certificate of Live Birth (CLB), SINASC’s foundational reporting form. The training process encompasses the development of educational materials, seminars, and both individual and group workshops. Additionally, healthcare facilities that conduct births and adhere to established standards of completeness and timely data entry receive annual certification through the "SINASC Seal," reinforcing quality assurance and data integrity.

Materials and Methods section

2. The objective of the study is to analyze the trends in Gestational Age at birth in the city of São Paulo. However, when considering births that occurred in the city of São Paulo, the total number of live births in the city of São Paulo is obtained, regardless of the mother’s place of residence. How can this fact affect the results and conclusions of the study? Therefore, I suggest two possibilities: to present the answer to this question in the limitations of the Discussion section, or to redo the analyses considering only live births of mothers residing in the city of São Paulo who gave birth in the city itself.

We analyzed births occurring in São Paulo city to assess municipal childbirth care provision, providing actionable data for health system managers. We added this information to the Methods section.

3. In Table 1, correct the excluded values of the variables “Gestational Age”, “birth weight” and “out of hospital births”, adding the values without information.

We added information on variables’ completeness to the Methods section.

4. I suggest adding a topic to describe the variables used in the study.

We added the description of the studied variables to the Methods section, as suggested.

5. Why was the variable “race/skin color of the mother”, available in SINASC, not included in the Prais-Winsten regression analysis? I suggest justifying or adding this variable.

The socioeconomic variable chosen for analysis was “maternal education". In future analysis we will consider other relevant variables, such as “race/skin color of the mother”.

6. I suggest standardizing the use of the term “Annual Percent Change (APC)” instead of “Percent change rate” in the Statistical analysis section.

We adopted the term “annual percent change", as suggested.

7. In lines 110-112, translate the sentence into English.

We apologize for that. The text was translated to English.

8. Correct the formula in line 113, replacing “e” with “10”.

We corrected the formula, as required.

9. Cite the version of the SPSS software.

We added the required information to the Methods section.

10. Cite and justify the application of the “t-test” in tables 3 and 4. Why was this statistical test not presented in table 6?

The t-test (for independent proportions) was used to assess differences in percentage change rates between the public and private sectors and the type of birth. We added this information to the Methods section.

11. Since ensuring quality information is an essential condition for the analysis of epidemiological indicators (proportions), I suggest calculating the completeness of the variables used in the study, in the period 2012-2019.

We added the information about the variables’ completeness to the Methods section, as requested. From 2012 to 2019, the variables’ completeness ranged from 98.9% to 100.0%.

Results

12. In tables 3, 4, 5, 6, I suggest "APC" instead of "rate" and adding the respective p values.

We reworked the tables, as suggested.

13. In lines 172-173, the authors report that “These reductions were more pronounced in the first four-year period (2012-2015)”. I suggest applying a statistical test to identify differences between the periods 2012-2015” and “2016-2019”.

Resposta

14. In line 183, correct the APC value “for vaginal births” .

We corrected the value.

In the period 2012-2015, the annual percent change in the proportion of caesarean births at 38 weeks was −4.1%, compared to 1.4% for vaginal births. This difference was statistically significant. For 39 and 40 weeks, there was a higher percentage increase in cesarean sections compared to vaginal deliveries, but this difference was not significant. The proportion of preterm births decreased across all gestational ages under 37 weeks. This reduction was greater in vaginal births.

15. In lines 208-209, the authors report that “Rates were higher among mothers aged 35 years and over and who had completed more than 12 years of education”. I suggest applying a statistical test to identify differences between age groups and educational levels.

We reworked the analysis to better describe the comparisons made.

16.- Why in Table 6 were the same analyses not performed for the periods “2012-2015” and “2016-2019”? I suggest standardization according to the results presented in Tables 3, 4 and 5.

We reworked all the tables, as suggested.

17. For Figures 2, 3, 4 and 5, I suggest applying a statistical test to identify differences in the proportions of the variables during the study period.

The figures were calculated based on the proportion of births occurring in each gestational week, illustrating the annual distribution of gestational age (GA) during the study period. After descriptive analysis, we performed statistical testing to assess trends and associated factors.

Discussion

18. The discussion section could be more in-depth, citing other studies with similar designs (ecological time-series study) that evaluated the same outcome (trends in GA at birth) in Brazil and other countries.

We added the required information and a new reference (AMYX et al., 2024), as suggested.

19. Included the limitations of ecological studies and other limitations of the analysis of Health Information Systems.

We added the required information.

20. I suggest including a paragraph in the discussion addressing how social inequalities in the city of São Paulo and the COVID-19 pandemic can affect the conclusions of the study.

The study period did not include the COVID-19 pandemic.

Attachment

Submitted filename: 05-05-2025_NOITE_REVISORES PLOS ONE.pdf

pone.0319307.s003.pdf (214.7KB, pdf)

Decision Letter 1

Leonardo António Chavane

20 Aug 2025

Trends in gestational age at birth in the city of São Paulo, Brazil between 2012 and 2019

PONE-D-25-03233R1

Dear Dr. Niy,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager®  and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support .

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Leonardo António Chavane, M.D., MPH, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: In line 200, correct the APC value for the period 2012 to 2015 according to Table 3. The APC was -52.8%. Please verify.

On line 209, correct the APC for vaginal births to -3.4%. Please check.

Reviewer #3: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy .

Reviewer #2: No

Reviewer #3: No

**********

Acceptance letter

Leonardo António Chavane

PONE-D-25-03233R1

PLOS ONE

Dear Dr. Niy,

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team.

At this stage, our production department will prepare your paper for publication. This includes ensuring the following:

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Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

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Kind regards,

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on behalf of

Dr. Leonardo António Chavane

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    Attachment

    Submitted filename: Comments.docx

    pone.0319307.s001.docx (13.5KB, docx)
    Attachment

    Submitted filename: 05-05-2025_NOITE_REVISORES PLOS ONE.pdf

    pone.0319307.s003.pdf (214.7KB, pdf)

    Data Availability Statement

    The database is fully available for consultation at the Harvard Dataverse Repository: https://doi.org/10.7910/DVN/PP2VVF.

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