Mechanical testing and non-linear viscoelastic modelling of the human placenta in normal and growth restricted pregnancies.

BACKGROUND

Intrauterine Growth Restriction (IUGR) is a disease where the placenta is unable to transfer enough nutrients to the fetus, limiting its growth, and resulting in high mortality and life-long morbidities. Current detection rates of IUGR are poor, resulting in limited disease management. Elastography is a promising non-invasive tool for the detection of IUGR, and works by detecting changes in the mechanical properties of the placenta. To date, however, it is not known whether IUGR placentas have different mechanical properties from normal ones, and thus investigating this is the first focus of the current study. The second focus is to evaluate and model the viscoelastic properties of the normal and IUGR placenta, so that it may be possible to improve elastography in the future by incorporating viscoelasticity.

METHODS

Cyclic uniaxial mechanical compression testing was conducted on post-delivery human placenta samples. 18 samples from 5 normal placentae and 12 samples from 3 IUGR placentae were tested. Viscoelastic models were fitted to the resulting experimental data.

RESULTS

Mechanical testing showed that IUGR placentae have reduced stiffness and viscosity compared to normal placentae. Linear viscoelastic models were unable to provide a good fit to the data, but non-linear viscoelastic solid (NVS) models could do so. The best performing model was a five parameters bi-exponential NVS model. Two of the five parameters appear to capture the differences between normal and diseased samples.

DISCUSSION

Our results demonstrate that IUGR placentae have different mechanical properties from normal placentae, and a five parameter bi-exponential NVS model can effectively describe the mechanical properties of the placenta in health and disease.