Preterm membranes are mechanically more resistant than term membranes.

Abstract

To compare the biomechanical properties of fetal preterm membranes (20+0weeks to 30+0weeks) to those of the term (37+0 to 41+0weeks). Amnion 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. From 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±0.005J/m-1 ; p=0.027) but not in the amnion (0.030±0.017 vs. 0.029±0.009J/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±0.031N; p=0.023). In inter-suture distance tests, no significant interaction was observed beyond 3mm, but the preterm chorion showed less interaction at 1-2mm distances. Preterm 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.