[Biomechanical characteristics of human fetal membranes. Preterm fetal membranes are stronger than term fetal membranes].

The purpose of this study was to determine the biomechanical characteristics of human fetal membranes (FM) throughout gestation. Biomechanical properties were determined for 115 FM of 23-41 weeks gestation using our previously described methodology. The areas of membrane immediately adjacent to the strongest and weakest tested spots were sampled for histomorphometric analysis. Clinical data on the patients whose FM were examined were also collected. FM less than 28 weeks gestation were associated with higher incidence of abruption and chorioamnionitis. Topographically FM at all gestations had heterogeneous biomechanical characteristics over their surfaces with distinct weak areas. The most premature membranes were the strongest. FM strength represented by rupture force and work to rupture decreased with increasing gestation in both weak and strong regions of FM. This decrease in FM strength was most dramatic at more than 38 weeks gestation. The FM component amnion-chorion sublayers were thinner in the weak areas compared to strong areas. Compared to term FM, preterm FM are stronger but have similar heterogeneous weak and strong areas. Following a gradual increase in FM weakness with increasing gestation, there is a major drop-off at term 38 weeks gestation. The FM weak areas are thinner than the stronger areas. Whether the difference in thickness is enough to account for the strength differences is unknown.