Does preconditioning lower the rupture resistance of chorioamniotic membrane?

Premature rupture of fetal membrane occurs in about 3% of all pregnancies. The physical integrity of chorioamnion (CA) membrane should be retained until delivery for a healthy pregnancy. To explore the effect of pre-conditioning and probe size on the mechanical properties of human chorioamniotic sac, the mechanical properties of 17 human chorioamniotic membranes, collected from cesarean delivery, were examined using biaxial puncture tests with and without preconditioning by different probe sizes. For preconditioned samples, the mean ± std. of ultimate rupture stress was calculated to be 1.73 ± 0.13, 1.61 ± 0.29 and 1.78 ± 0.26 MPa for the probe sizes of 3, 5 and 7 mm, respectively. For samples with no preconditioning, these values were calculated to be 2.38 ± 0.29, 2.36 ± 0.37, and 2.59 ± 0.43 MPa for the above-mentioned probe sizes. The force to probe diameter for samples with no preconditioning was in the range of 1087-1301 N/m for the three probe diameters, well in the range of 850-1580 N/m reported by previous studies. Our results show that the preconditioned samples had significantly lower ultimate puncture force and ultimate stress compared to non-preconditioned samples. In addition, a correlation between the probe size and the magnitude of puncture force was observed, while the stress values were not significantly affected by changing probe size.