171 Introduction Contractions of the uterus during labour have been extensively studied and is basic knowledge amongst the population. On the contrary, knowledge of these wave-like motions (peristaltic contraction and relaxation of the subendometrial layer) outside pregnancy is relatively unknown and research into its characteristics has been hampered by the subjectivity of the available measurement tools (233). Today, no comprehensive and fully objective measurement tool is widely used. Multiple methods have been used to visualise and analyse uterine contractions and its different characteristics (233). Intra-uterine pressure (IUP) measurement using a catheter is a precise method which is able to measure contraction frequency, direction and amplitude; however, the introduction of the catheter itself may influence the natural behaviour of the uterus. Measuring contraction direction is also not feasible when using one single(lumen) catheter (234). Transvaginal ultrasound (TVUS) is another method that can visualize uterine contractions (69). TVUS investigation, and the subsequent analysis of the imaging loops, can however be subjective due to a dependence on the observer’s sonographic skills and ability to interpret the TVUS recordings. Furthermore, although several peristalsis parameters (e.g., frequency and direction) can be assessed on TVUS it is not possible to quantify the amplitude of the waves. Another way to visualize uterine contractions is hysterosalpingoradionuclide scintigraphy (HSSG). It is excellent for demonstrating the contraction direction, however contraction amplitude and frequency cannot be assessed by HSSG. Recent studies have also used MRI to visualize and assess contractions (233). The so-called cine MRI is used to visualize peristalsis of the uterus in real-time (235). Similar to TVUS and HSSG, and despite its cost and sophistication, the evaluation of contraction amplitude is not possible by MRI (233). In a healthy uterus, rhythmic contractions change in intensity as well as direction during the menstrual cycle to support sperm propagation and embryo implantation in response to hormonal variations (236). Other characteristics of uterine contractions - frequency and amplitude - are altered throughout the menstrual cycle as well (237). During menstruation for instance, uterine contractions are directed with high amplitude and low frequency from the uterine fundus to the cervix, whereas the periovulatory
RkJQdWJsaXNoZXIy MTk4NDMw