Design, Development and Testing of Cervical Dilatation Measurement System

Abstract

Monitoring labour progression is of utmost importance, to avoid complications during childbirth. Frequent monitoring allows prevention, identification, and management of complications during childbirth. Improper monitoring can result in serious complications and can negatively impact the health of both the mother and the baby. The problems get exaggerated in remote villages due to lack of medical infrastructure and timely transportation. The parameters that are commonly monitored during labour are frequency, strength and duration of uterine contractions, cervical effacement and dilatation, and foetal head station. Cervical dilatation is one of the most important parameters used to gauge the progress of labour. Monitoring cervical dilatation alone, allows healthcare professionals to take decisions regarding subsequent intervention.

Digital trans-vaginal examination, when conducted by an experienced practitioner, is considered the gold standard for obstetric practice. However, the measurement is inaccurate due to inter and intra-observer variability. The variability results from the fact that the cervix is soft and can get easily stretched during measurement. Patients, especially the ones with ruptured membranes, are put at heightened risk of infections when subjected to repeated vaginal examinations and they also experience discomfort.

In an attempt of improving the accuracy of measurement, different methods have been explored in literature. Various mechanical measurement tools that were devised were found to be heavy and caused distortion of the cervix. Ultrasonic monitoring methods require the sensors to be screwed into the tissue at the exact locations. This may lead to local trauma and any error in sensor placement could lead to increased measurement errors due to which this may not be the preferred method of measurement for cases of normal labour. While high-resolution, real-time ultrasound imaging systems are available, they are prohibitively expensive. None of the methods mentioned above have managed to reach a hospital setting.

The aim of this work is to develop a cervical dilatation measurement system which is accurate, cost-effective, safe, and easy to use, and causes least discomfort to the patient. It is desired that the sensing mechanism used for measurement be non-contact in order to reduce patient trauma. Hence, imaging using cameras is explored in this work. Through extensive literature study of the complex and dynamic anatomy of the female reproductive system, it is established that the vaginal canal may occlude any non-contact sensor placed at the vaginal introitus. In order to support measurement by any such sensor, a mechanism is required to retract the vaginal walls. Various existing vaginal retractors, also called specula, are evaluated and a novel retractor is designed to suit cervimetric applications, such that it provides maximal cervical visibility while causing minimal patient discomfort. The materials used in the manufacturing of the retractor and the manufacturing process is also discussed. This retractor is evaluated to be safe for use within the vaginal environment.

Images of the dilating cervix are studied. Various image processing techniques such as manual, colour-based, and edge-based detection methods are established and evaluated for the detection of the cervical os. A consolidated image processing tool is also developed and guidelines for choice of image processing parameters are established.

The specifications of the camera system required for use in cervimetry are determined. Two types of camera systems: monocular and stereo systems are developed in this work. The bio-compatible packaging of these systems is discussed. These systems are tested on cervical models and evaluated for use in cervimetry. It is found that endoscopic imaging in cervimetry performs better than most of the state-of-the-art cervimetric methods found in literature. Overall, a cervimetric product which utilizes an imaging device and a supporting retractor, along with associated image processing has been developed in this work with the intention of its long-term and sustained utilization in a clinical setting.