OBJECTIVE:
    Spontaneous rupture of the fetal membranes occurs after the commencement of labor in 90% of cases. Recent evidence indicates that the process of parturition requires not only an increase in myometrial contractility and cervical ripening, but also degradation of extracellular matrix in fetal membranes (i.e., leakage of fibronectin into cervico-vaginal secretions). This study was undertaken to determine if parturition is associated with in vivo evidence of increased bioavailability of matrix metalloproteinases-9 (MMP-9) and its inhibitor, tissue inhibitor of metalloproteinases-1(TIMP-1).

METHODS:
    A cross-sectional study was conducted with women in the following categories: 1) midtrimester (n = 25); 2) preterm labor and intact membranes in the absence of intraamniotic infection (n = 78); 3) term not in labor (n = 25); and 4) term with intact membranes in labor (n = 25). MMP-9, and TIMP-1 were measured using sensitive and specific immunoassays.

RESULTS:

1. Spontaneous labor at term was associated with a significant increase in MMP-9 but not in TIMP-1.
2. Women with preterm labor who delivered prematurely had significantly higher concentrations of MMP-9 but not TIMP-1 in amniotic fluid than those with preterm labor who delivered at term.
3. The concentrations of TIMP-1 decreased with advancing gestational age. In contrast, MMP-9 concentrations did not change with advancing gestational age.

CONCLUSIONS:
    Spontaneous human parturition is associated with specific changes in the enzymatic machinery responsible for extracellular matrix degradation.