['The purpose of this study was to determine whether acute repetitive stretching causes fetal membranes (FM) weakening.', 'Cesarean or vaginally delivered FM were repeatedly stretched and thereafter subjected to rupture testing. Rupture strength (RS), work to rupture (WR), and stiffness were determined. Unstretched FM were compared with stretched FM.', 'In the cesarean group, FM stretched to 50% or 75% of the baseline (unstretched) RS for 10-20 cycles of 10 seconds each paradoxically showed increased RS and stiffness. WR decreased compared with baseline. Detailed analysis revealed that even a single stretch cycle initiated these changes to physical properties. Vaginally delivered FM showed similar changes in physical properties, as did separated amnion.'] Does the force required to rupture fetal membranes paradoxically increase with acute in vitro repeated stretching?