Patients with ruptured membranes usually note a large “gush of fluid” that wets their undergarments or bed sheets. Rather, their use should be restricted to situations in which the results of the examination clearly will influence clinical management. 8 However, in view of the multiple experiments cited previously that confirmed the effect of bacteria and bacterial proteases on membrane integrity, antenatal cervical examinations should not be performed as a matter of routine from 37 weeks until onset of labor. McDuffie and associates 9 were unable to explain precisely why their results differed so markedly from those of Lenihan. Moreover, they noted no significant differences in the frequency of cesarean delivery, oxytocin administration for induction or augmentation of labor, incidence of chorioamnionitis, or neonatal sepsis. These authors observed no significant differences in the frequency of PROM or prolonged rupture of the membranes (ROM).
Half the patients received weekly cervical examinations from 37 weeks to delivery, and half had no examinations until onset of labor. In a follow-up to Lenihan’s investigation, McDuffie and associates 9 randomly assigned 604 term patients to two groups. The cesarean delivery rate was similar in the two groups. Eighteen per cent of women in the group being examined experienced PROM compared with 6% in the latter group ( p = 0.001). One hundred and seventy-five women were assigned to the “no examination” group. He conducted a prospective investigation of 349 uncomplicated term patients, 174 of whom were randomly assigned to receive weekly cervical examinations from 37 weeks to delivery. In support of this hypothesis, Lenihan 8 confirmed that antenatal cervical examinations were associated with an increased frequency of PROM.
The clinical implication of these observations is that certain interventions, such as digital examination of the cervix, may increase the risk of bacterial contamination of the membranes and, simultaneously, increase the risk of PROM.
In a similar model, Schoonmaker and coworkers 7 demonstrated that exposure of fetal membranes to group B streptococci, Staphylococcus aureus, or activated neutrophils and neutrophil elastase resulted in significant decreases in membrane strength, elasticity, and work to rupture. Sbarra and colleagues 6 observed that growth of Escherichia coli and group B streptococci on the decidual surface of fetal membranes significantly weakened the tensile strength of the membranes compared with uninfected control membranes. McGregor and associates 5 demonstrated that, when fetal membranes were exposed to bacteria or to bacterial collagenases, the bursting load, elasticity, and work to rupture were significantly reduced. Several lines of evidence suggest that bacterial colonization can reduce the tensile strength of membranes and, thereby, predispose to rupture. The role of infection in the etiology of PROM is clearly of great importance. Collagen synthesis was also lower in these membranes. Collagenolytic activity and collagen solubility were higher in membranes that ruptured prematurely. Similarly, Vadillo-Ortega and co-workers 4 measured collagen content, acid-soluble collagen, collagen degradation activity, and collagen biosynthesis in 22 normal and 20 prematurely ruptured membranes from patients at 37 weeks’ gestation or later. For example, Artal and colleagues 3 showed that prematurely ruptured membranes had definite decreases in thickness and elasticity at the site of rupture.
Membranes that rupture prematurely may have different mechanical properties to those that do not rupture prematurely. In a survey of data from the Collaborative Perinatal Project, Naeye 2 demonstrated an association between cigarette smoking and PROM in term patients. Conditions that overdistend the uterus, such as multiple gestation and polyhydramnios, may predispose to PROM.
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