Microstructure and mechanics of the chorioamnion membrane with an emphasis on fracture properties

The normal mechanical functioning of an intact chorioamnion (CA) membrane is essential to successful human reproduction. The amnion and the chorion, separately and together as the bilayer chorioamnion, serve barrier and container functions throughout gestation, and these two important roles are required from conception to birth. The event associated with the "breaking of waters" is a landmark event in labor and delivery. Mechanical rupture of the CA membrane is part of the natural sequence of term delivery, but has serious implications when rupture occurs prior to term; preterm premature rupture of the CA membrane (PPROM) is associated with one-third of premature births. The current manuscript reviews PPROM from a clinical, anatomical, and mechanical perspective with a special focus on the clinically relevant fracture properties of these membranes. Emphasis is given to the link between membrane structure and properties at macroscopic and microscopic length scales. Because it has been demonstrated that the mechanical properties of prematurely failed membranes are not different from membranes of the same gestational age that have remained intact, membrane failure is a local process that must be explored in terms of local changes in structure and properties of isolated portions of the membrane. Future diagnostic techniques aimed at detection of changes in membrane structure (including thickness) and altered mechanical stiffness or strength may allow for prefailure diagnosis of membrane weak spots, thus opening the door for potential intervention and treatment techniques for preterm membrane rupture.