FIGURE 1.

Mechanical stretch and subsequent leukocyte infiltration are essential for labor onset at term. Step 1: Mechanical stretch synergistically augmented leukocyte infiltration and production of pro-inflammatory chemokines via the NF-κB pathway. Step 2: The entry of amniotic fluid components into uterine vasculatures promoted myometrial infiltration with macrophages and neutrophils. Step 3: Infiltrating leukocytes could induce expression of pro-inflammatory cytokines and PGs through the activation of NF-κB. Step 4: The final step is the progressive uterine contractility and resultant term birth. We hypothesized that the initial wave of mechanical stretch and leukocyte infiltration would be followed by the second big wave of sterile inflammation and subsequent myometrial contraction.