Causal effect of hypertensive syndromes during pregnancy on prematurity: data from cross-sectional study “Born in Brazil”

Abstract To evaluate the causal effect of hypertensive syndromes during pregnancy (HSP) on prematurity. Data were obtained from the nationwide study “Born in Brazil” (“Nascer no Brasil”), conducted with 23,894 women. Hypertensive syndromes comprised the synthesis of positive responses to any of the questions relating to increased blood pressure contained in the questionnaires completed with data from patients’ hospital records and prenatal cards. The outcome was early and late preterm birth. The confounding variables were indicated in the directed acyclic graph, and the causal effect was estimated by the propensity score. Of the 20,494 postpartum women evaluated in this study, 2,369 presented a diagnosis of hypertensive syndromes, and among these, 5.8% were early premature births and 13.5% were late premature births. After weighting, women with hypertensive syndromes had a 2.74-fold greater chance of having an early preterm birth (ORadj: 2.74; 95%CI: 2.12-3.54) and a 2.40-fold greater chance of having a late preterm birth (ORadj: 2.40; 95%CI: 1.86-3.08). The causal effect of hypertensive syndromes on prematurity reaffirmed their role in causing an increase in premature births, reinforcing the importance of controlling syndromes during prenatal care.