A PATIENT-SPECIFIC STUDY TO INVESTIGATE THE MECHANICAL FUNCTIONS OF UTERUS AND CERVIX ON PRETERM BIRTH IN A PREGNANT WOMAN

Preterm labor is a complex process affected by several factors through which cervical failure plays a vital role in some patients. During the pregnancy, the proper cervical function is required to maintain the fetus in the uterus. Softness and shortness of the cervix are two main causes of preterm delivery.  The aim of this study was to investigate the effect of the cervical softening and deformation of amniotic sac on mechanical function of the cervix under the organ mechanical environment.

A 3D model of the uterus, cervix, and fetal membrane of a pregnant woman was built based on MR imaging in order to analyze the mechanical function of the uterus and cervix under physiological loading of pregnancy. In this study, to describe the collagenous tissue of the uterus and cervix, a hyperelastic composite material with a neo-Hookean ground substance assuming a continuous random fiber distribution was used. The effect of cervical remodeling on preterm delivery was studied using two types of fibers, pregnant, soft, and deformed, and non-pregnant, rigid and non-deformed. Also, the geometrical effects of amniotic sac have been studied by assuming two different geometries for amniotic sac which are deformed, and non-deformed. Behavior of tissue deformation resulted from stress, changes in the geometry of the organs and the interaction between the uterus, cervix and fetal membrane have been studied using finite element method and patient-specific geometry based on previous experimental and numerical investigations.

The amount of stress obtained at the front part of the internal mouth of the cervix of the basic model, the part where the highest concentration of stress and deformation occurred, as predicted by previous studies is approximately 5 kPa. In other models, the effective stress is less than this value, and is at least equal to 5.3 kPa. The strain rate in the soft cervical model and the deformed amniotic sac was higher than other models because both causes of early delivery exist simultaneously.

The present model shows that changes in the geometry of amniotic sac increase the load on the cervix and initiates the funneling. Funneling is a process in which the initial dilation of the cervix causes the production of chemical signals by the cervix smooth muscle cells causing further cervical dilatation and ultimately cervical insufficiency, which is one of the most important causes of preterm labor.