Fatores associados ao nascimento prematuro incidente, recorrente e termo precoce no Brasil

Abstract

Introduction: The adverse consequences of preterm birth (PTB) and early term can be observed in the short and long term. PTB is a complex syndrome resulting from sociodemographic, psychosocial, nutritional, behavioral and biological factors. A previous PTB is considered the most important predictor for a subsequent NP. Studies have shown that risk factors for early-term birth are similar to those for PTB, with emphasis on cesarean section (CS). Although several studies have examined the risk factors associated with recurrent PTB, few studies assess, at the same time, the factors associated with incident and recurrent PTB. Studies evaluating the association between CS and early-term birth are also limited, especially in low- and middle-income countries. General objective: To assess the factors associated with incident and recurrent PTB and early-term birth among live births in Brazil. Specific objectives: 1) Develop a hierarchical theoretical model of PTB determinants; 2) Estimate the associations between the previous PTB and the recurrence of the PTB; 2) Investigate the recurrence of preterm birth in the Center for Data and Knowledge Integration for Health (CIDACS) birth cohort; 3) Explore whether risk factors for preterm birth are different according to the gestational age of the previous birth (term or preterm); 4) Investigate the association between CS and early-term birth according to the Robson Classification. Methods: The thesis was presented in four articles according to each specific objective. To carry out the first article, a hierarchical theoretical model of the PTB determinants was proposed, which describes the interrelationships between the variables in each level of its determination (distal, intermediate, and proximal). The second and third articles were developed with data from the CIDACS birth cohort, based on the theoretical model developed on the previous objective. This cohort was created by linking data from the National System of Live Births in Brazil (SINASC) and the 100 Million Brazilians Cohort baseline for the period from January 1, 2001, to December 31, 2015. In article 2, PTB was defined as birth with less than 37 weeks of gestation. Multivariate logistic regression was used to estimate the association between PTB in the first pregnancy and the subsequent PTB. In article 3, incident PTB was defined as a live birth with a gestational age less than 37 weeks and preceded by a previous full-term birth; and recurrent PTB was defined as live birth with a gestational age less than 37 weeks preceded by a previous PTB. Longitudinal transition model with logistic regression was used to investigate whether risk factors varied between incident and recurrent PTB. For the development of the 4th article, a population-based cross-sectional study was conducted with routine data from SINASC, from 2012 to 2019. Women of reproductive age were classified into one of the ten Robson groups based on characteristics of pregnancy and delivery. Propensity scores were used to match women who had cesarean sections with women who had vaginal deliveries (1: 1). Logistic regression was used to assess the association between cesarean section and early-term. Results: In the second article, 3,528,050 live births were evaluated. The adjusted odds for the recurrence of a PTB was 2.58 (95% confidence interval [CI] 2.53–2.62). Lower gestational ages in a previous pregnancy increased the odds of a subsequent PTB (<28 weeks: adjusted OR [aOR] 3.61, 95% CI 3.41– 3.83; 28–31 weeks: aOR 3.34, 95% CI 3.19–3.49; and 32–36 weeks: aOR 2.42, 95% CI 2.38– 2.47). Women who had two previous PTBs were at high risk of having a third (aOR 4.98, 95% CI 4.70–5.27). Recurrence of PTB was more likely when the interbirth interval was less than 12 months. In the second article, different risk factors for incident and recurrent PTB were identified. The following factors were associated with an increased chance for PTB incidence, but not recurrence: household overcrowding (aOR 1.09; 95% CI 1,07-1,10), maternal race/ethnicity [(black/mixed: aOR 1.04; 95% CI 1.03-1.06) and (indigenous: aOR 1.34; 95% CI 1.24-1.44)], young maternal age (14–19 years: aOR 1.16; 95% CI 1.14-1.18), and cesarean delivery (aOR 1.09; 95% CI 1.08-1.11). The following factors were associated with both incident and recurrent PTB, respectively: single marital status (OR 0.85; 95% CI 0.84-0.86 vs 0.90; 95% CI 0.87-0.93), reduced number of prenatal visits [(No visit: aOR 2.56; 95% CI 2.47- 2.66 vs aOR 2.16; 95% CI 1.98-2.36) and (1–3 visits: aOR 2.44; 95% CI 2.40-2.49 vs OR 2.24; 95% CI 2.14-2.33)], short interbirth intervals [(12–23 months: aOR 1.04; 95% CI 1.02-1.06 vs aOR 1.22; 95% CI 1.17-1.26), and (<12 months: aOR 1.89; 95% CI 1.80-1.98 vs aOR 2.58; 95% CI 2.38-2.79)], and advanced maternal age (35–49 years: aOR 1.42; 95% CI 1.38-1.47 vs aOR 1.45; 95% CI 1.33-1.58). For most risk factors, the point estimates were higher for PTB incidence than recurrence. In the fourth article, 17,081,685 live births were included. Births by CS had higher odds of early-term birth (aOR 1.32; 95% CI 1.32-1.32) compared with vaginal deliveries. Births by CS to women in groups with low clinical need and expected rate of CS showed the highest odds of early term compared with vaginal deliveries: group 2 (aOR 1.50; 95% CI 1.49–1.51) and group 4 (aOR 1.57; 95% CI 1.56-1.58). Increased odds of early-term births were also observed among births of women in group 3 (aOR 1.30; 95% CI 1.29–1.31). Also, births from women with a previous CS (Group 5: aOR 1.36; 95% CI 1.35–1.37), single breech pregnancy [(Group 6: aOR 1.16; 95% CI 1.11-1.21) and (Group 7: aOR 1.19; 95% CI 1.16-1.23)], and multiple pregnancies (Group 8: aOR 1.46, 95% CI 1.40–1.52) had high odds of an early-term birth. Conclusion: These articles present important information regarding the factors associated with incident and recurrent preterm birth and early-term birth in Brazil. The results can contribute to the development of intervention strategies and implementation of public policies aimed at reducing PTB in a subsequent pregnancy and reducing the excessive number of clinically unnecessary cesarean sections which will allow the reduction in the number of early-term births.