The median maternal plasma fragment Bb concentration was higher in patients with PTL who delivered preterm, either with IAI (1.21 μg/ml, IQR 0.77-2.16 vs. 0.86 μg/mL, IQR 0.64-1.57; p=0.007) or without IAI (1.13 μg/mL, IQR 0.92-2.08; p=0.026), than those with an episode of PTL who delivered at term and than those with a normal pregnancy (p<0.001 for both comparisons).