Soto et al. reported that women with preterm labor and intra-amniotic infection have higher median maternal plasma C3a and C5a levels than those with preterm labor without intra-amniotic infection, whereas there was no difference in the plasma C3a and C5a levels between women with preterm labor who delivered at term and those with preterm delivery (< 37 weeks) [18]. This evidence concerns the gene C3 and chorioamnionitis.