form that is crucial to ripening. The two forms of collagen have a different fluorescent pattern that can be monitored by a collascope. Garfield reported that in humans and rats there is a decline in the fluorescent pattern of the cervix as parturition nears, which corresponds to the change in type I collagen. Further, they were able to show in patients that when the fluorescent patterns decrease due to changes of collagen content, the cervix softens and the patient will deliver preterm.
The biochemical pathway resulting in the breakdown in the cervical matrix has been extensively studied (see Uldbjerg 1989; Leppert,1995, for review). These pathways can be activated by a number of external compounds and provide possible sites of interactions for environmental factors to play a role. The activation of prostaglandins and the subsequent activation of compounds such as NO constitute an area of ongoing research. The role of NO appears to have different effects in activating the myometrium or softening the cervix, according to Garfield. NO levels are elevated in the uterus (as discussed previously) during pregnancy and are associated with uterine quiescence. At the onset of labor, production of NO decreases, resulting in an increase in uterine contractility. In contrast, NO production increases in the cervix as labor begins and appears to be involved in softening of the cervix. Similar results (cervical softening) have been obtained by locally applying NO agonists to the cervix.
The fetal membranes, which surround the amniotic cavity, are composed of two layers: the amnion and the chorion. The primary function of the membranes is to retain the amniotic fluid, to secrete substances into the fluid and the uterus, and to protect the developing fetus from infection. Rupture of the membranes is the third event necessary for delivery, and it occurs shortly before parturition begins. Preterm rupture of the membranes occurs in approximately 1 percent of all pregnancies and is associated with 30–40 percent of all preterm deliveries.
Preterm rupture of the membranes occurs in approximately 1 percent of 23 pregnancies and is associated with 30–40 percent of all preterm deliveries.
Fetal fibronectin is a protein, which is part of the extracellular matrix between the membranes and the decidua. It is used as a marker of impending labor, especially preterm birth. When an inflammation or breakdown of the extracellular matrix occurs, fibronectin leaks down into the cervix and the vagina. Goldenberg stated that women in early preterm labor with a negative fetal fibronectin test have a less than 1 percent chance of delivering in the subsequent two weeks.