Stress Relaxation, Used as a Tool for Diagnosis of Incompetence of Human Cervix in Terms of a Mixture Model of Tissue

Abstract

Cervical incompetence, that is failure of the cervix uteri to remain closed under the load of the developing embryonic sac, is one of the main causes of second-trimester abortion and premature delivery. A cervix known to be incompetent may be treated by suturing it all the way around with a synthetic fibre. However, there is a lack of a reliable technique to assess the diagnosis directly, i.e. based on the determination of the mechanical properties of the cervix. It is known that the mechanical properties change during pregnancy under the influence of hormones. Therefore one may doubt whether measurements done outside pregnancy, which clinically is preferable, is likely to be of value in predicting incompetence. Nevertheless Van Duyl et al. (1) published a retrospective study on non-pregnant women with cervices known to be incompetent and volunteers with normal cervices, that relaxation measurements yield parameters which permit a high level of discrimination between competent and incompetent. The technique is based on observation of stress relaxation after stepwise dilatation of the cervical canal by means of a cylindrical shaped nylon, i.e. almost inelastic, balloon. After insertion into the canal the balloon is inflated by filling it fastly with saline by means of an infusion pump until a reference pressure of 33 kPa is reached.