Abstract
The fetal membrane surrounds the fetus during pregnancy and is a thin tissue composed of two layers, the chorion and the amnion. While rupture of this membrane normally occurs at term, preterm rupture can result in increased risk of fetal mortality and morbidity, as well as danger of infection in the mother. Although structural changes have been observed in the membrane in such cases, the mechanical behaviour of the human fetal membrane in vivo remains poorly understood and is challenging to investigate experimentally. Therefore, the objective of this study was to develop simplified finite element models to investigate the mechanical behaviour and rupture of the fetal membrane, particularly its constituent layers, under various physiological conditions. It was found that modelling the chorion and amnion as a single layer predicts remarkably different behaviour compared with a more anatomically-accurate bilayer, significantly underestimating stress in the amnion and under-predicting the risk of membrane rupture. Additionally, reductions in chorion-amnion interface lubrication and chorion thickness (reported in cases of preterm rupture) both resulted in increased membrane stress. Interestingly, the inclusion of a weak zone in the fetal membrane that has been observed to develop overlying the cervix would likely cause it to fail at term, during labour. Finally, these findings support the theory that the amnion is the dominant structural component of the fetal membrane and is required to maintain its integrity. The results provide a novel insight into the mechanical effect of structural changes in the chorion and amnion, in cases of both normal and preterm rupture.
Highlights
The fetal membrane is a thin tissue that surrounds the fetus during gestation, and is critical for maintaining a pregnancy to delivery [1]
ROM occurs before the onset of labour, known as premature rupture of the membrane (PROM), which is not considered to be pathological as it is usually followed by contractions [2, 3]
Modelling the mechanics of the chorion and amnion pregnancies are affected by rupture earlier than 37 weeks gestational age, known as preterm premature rupture of the fetal membrane (PPROM) [3]
Summary
The fetal membrane is a thin tissue that surrounds the fetus during gestation, and is critical for maintaining a pregnancy to delivery [1]. ROM occurs before the onset of labour, known as premature rupture of the membrane (PROM), which is not considered to be pathological as it is usually followed by contractions [2, 3]. Modelling the mechanics of the chorion and amnion pregnancies are affected by rupture earlier than 37 weeks gestational age, known as preterm premature rupture of the fetal membrane (PPROM) [3]. PPROM is the cause of one third of all premature births [4], and is associated with increasingly high risk of mortality and morbidity with earlier gestational age [3]. While multiple other risk factors for PPROM have been identified, notably cases of abnormally low (oligohydramnios) and abnormally high (polyhydramnios) volumes of amniotic fluid in the uterus [6, 7], the specific causes of PPROM remain poorly understood and study of the changes in the mechanical behaviour of the fetal membrane that underlie PPROM is ongoing [8]
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