Preterm membranes are mechanically more resistant than term membranes

ObjectiveTo compare the biomechanical properties of fetal preterm membranes (20 + 0 weeks to 30 + 0 weeks) to those of the term (37 + 0 to 41 + 0 weeks).MethodAmnion and chorion were manually separated and samples were cut to the required geometry. Rectangular samples with (mode 1) and without (uniaxial) a notch, were tested for tearing energy, critical elongation, and tangent stiffness. Suture retention and inter-suture distance testing investigated the effect of suture placement.ResultsFrom the 15 preterm and 10 term placentas studied, no notable differences were observed in uniaxial testing. Mode 1 fracture testing showed a difference in tearing energy between the preterm and term chorion (0.025 +/- 0.005 vs. 0.017 +/- 0.005 J/m-1; p = 0.027) but not in the amnion (0.030 +/- 0.017 vs. 0.029 +/- 0.009 J/m-1; p = 0.895). Both preterm amnion and chorion showed a higher critical elongation compared with term (1.229 +/- 0.057 vs. 1.166 +/- 0.046; p = 0.019 and 1.307 +/- 0.049 vs. 1.218 +/- 0.058; p = 0.012). Preterm amnion had a higher suture retention strength than its term counterpart (0.189 +/- 0.065 vs. 0.121 +/- 0.031 N; p = 0.023). In inter-suture distance tests, no significant interaction was observed beyond 3 mm, but the preterm chorion showed less interaction at 1-2 mm distances.ConclusionPreterm membranes have equivalent or superior tensile properties to term membranes. The chorion appears to contribute to the mechanical integrity of fetal membranes, particularly in preterm stages. What is already known about this topic?Iatrogenic preterm rupture of membranes after prenatal interventions remains problematic, often leading to preterm delivery.Previous biomechanical research showed that fetal membranes have unique properties that prevent rupture, yet data on preterm membranes are lacking.What does this study add?Preterm membranes have equivalent or superior mechanical properties to term membranes.The chorion layer appears to contribute to the mechanical integrity of fetal membranes, particularly in preterm stages.