Regulatory Cytokine Expression and Preterm Birth: Case-Control Study Nested in a Cohort

BACKGROUND Currently known risk factors explain only a small fraction of preterm birth (PTB). Previous PTB is one of the most important predictors. However, this information is not available in primiparous women. Few studies have looked at associations between regulatory cytokine expression (RCE) and PTB and the results are conflicting. OBJECTIVE To investigate the association of RCE-Interleukin 10 (IL-10) and Transforming Growth Factor β (TGF-β)-with PTB, and to assess whether bacterial vaginosis (BV) is involved in this relationship. METHODS This was a case-control study nested in a prospective cohort-called BRISA. Women with singleton pregnancies were interviewed from 22 to 25 weeks of gestational age (GA). Women were recruited from health services in São Luís, Brazil. A blood sample was collected and gynecological examination was performed. Serum IL-10 and TGF-β were determined using cytometric bead array. Nugent score >7 and/or the presence of clue cells were used for BV diagnosis. All PTB estimated by ultrasound dating performed before 20 weeks of gestational age were considered cases. Controls were selected by simple random sampling from the rest of the cohort, at a 2:1 ratio. Different models were tested, according to the main independent variable. Odds ratios (OR) and 95% confidence intervals (95%CI) were estimated by regression analyses. RESULTS The study included 327 pregnant women, 109 cases and 218 controls. No associations were found between BV and PTB (P = 1.44; 95%CI: 0.51-3.77). Low levels of IL-10 (OR = 2.92 95%CI: 1.38-6.16) or TGF-β (OR = 16.90 95%CI: 6.42-44.51) or both simultaneously (OR = 77.16 95%CI: 7.99-744.88) were associated with increasing odds of PTB, even after adjustment for confounding. CONCLUSION Decreased RCE is a risk factor for PTB. This relationship, however, is not triggered by the presence of BV. Low IL-10/TGF-β levels from 22 to 25 weeks of GA could be used as early predictors of PTB. We suggest monitoring of these RCE, especially among primiparous women, for whom history of previous PTB is not available.