Low concentrations of thrombin-inhibitor complexes and the risk of preterm delivery

High maternal concentrations of thrombin-antithrombin (TAT) complexes have been associated with adverse outcomes. The objective of this study was to evaluate the relationship between TAT in asymptomatic subjects at 24 and 28 weeks and spontaneous preterm birth (SPTB).

A secondary analysis of the National Institute of Child Health and Human Development Preterm Prediction Study was performed. Subjects with SPTB were matched to controls. Maternal TAT concentrations were previously measured at 24 and 28 weeks. Differences between cases and controls were analyzed with Mann-Whitney U and logistic regression.

TAT was lower in cases than controls at 28 weeks (P = .01). The odds ratio for SPTB with TAT less than 25% was 2.55 (95% confidence interval, 1.34-4.89) when adjusted for clinical variables.

Early third-trimester TAT was lower in subsequent cases of SPTB. In some patients, low TAT concentrations may represent impaired thrombin activation and be pathologic.