Full-term and prematurely ruptured fetal membranes

Abstract

The layers of the human amnion and chorion were examined by light and transmission electron microscopy. Comparisons among different anatomical sites with respect to full-term and prematurely ruptured membranes indicate that (a) the thickness of the membranes is reduced near the rupture point; (b) intercellular canals near the implantation site become dilated and branched; (c) the trophoblast layer of full-term membranes is thinner and with more degenerating cells; and (d) the fibroblast and spongy layers have fewer collagenous fibers and less organization near the rupture site. These findings suggest that, although cellular activity is maintained in prematurely ruptured membranes, the mainly collagenous extracellular matrix undergoes marked disorientation. If this occurs too early in gestation, it may lead to premature rupture.

Striking Changes in the Structure and Organization of Rat Fetal Membranes Precede Parturition1

“…Al-Zaid and Bou-Resli [41], Evaldson et al [42], Halaburt et al [43], and Yoshida and Manabe [44] report that neither term human fetal membranes nor those that ruptured prematurely had decreased amounts of collagen compared to earlier stages. In contrast, Skinner and coworkers [33,34] and Bou-Resli et al [32] found that total collagen as well as the number of collagen fibrils decreased as birth neared in full-term and prematurely ruptured human fetal membranes. These disparities may be reconciled by the recent findings of Malak and Bell [6] who, using a quantitative structural approach, identified a zone of highly altered morphology that was of limited distribution along the rupture site in recently delivered term human placentas.…”

“…The authors believe this zone to be the initial site at which rupture occurs. This notion gains support from the findings that 1) disruption of connective tissue collagen was present only in areas adjacent to the rupture site in human fetal membranes that ruptured prematurely [32] and 2) decreased amounts of soluble collagen occurred only in the region of the rupture site in human chorions obtained at term delivery [9].…”

“…Moreover, the viscous material we observed clinging to rat fetal membranes on Day 21 of gestation may well represent the sugar-containing GAGs that they lose at this time. It is germane that human fetal membranes also suffer a loss of collagen and GAGs as gestation ends [32][33][34]. Taken together, the changes in connective tissue collagen and associated GAGs/proteoglycans described in this and the preceding paragraph probably account for the increased "bagginess" of rat amnion and VYSP on Day 21 of pregnancy.…”

Term Human Fetal Membranes Have a Weak Zone Overlying the Lower Uterine Pole and Cervix Before Onset of Labor1

“…None of the groups that conducted extensive investigation of FM physical properties reported correlations with tissue biochemical or histological characteristics. Two studies of collagen content and FM physical properties failed to show any association [19,20]. Schoonmaker et al [31] demonstrated that in vitro incubation of FM with high concentrations of bacterially derived collagenase or proteinase-producing bacteria weakened the membranes.…”

“…This testing procedure most closely mimics the in situ physiological stretching of FM over an open cervix. However, it is logistically difficult and requires relatively large pieces of FM for each test, allowing only one or two fragments per placenta to be examined [12][13][14][18][19][20][21]. Puncture testing, which is described in Materials and Methods, was initiated because of the problems associated with other methodologies.…”