165 DISCUSSION: The results of this exploratory study suggest a preliminary range of normal reference values in a healthy population of women without hormonal contraception and normal uteri. We present a novel, reproducible and objective method based on ultrasound speckle tracking. We are able to characterise uterine contraction amplitude and frequency, as well as coordination, direction, and velocity. Coordination, direction, and velocity of uterine contractions are features that have never before been quantified in this context. Our results show that contraction frequency and velocity are highest in the late follicular phase and lowest in the menstrual and late luteal phase. Coordination seems to be negatively affected by contractions with higher frequency and velocity in the late follicular phase compared to other phases. Amplitude and contraction direction in this population do not show significant variations across the menstrual cycle. Our findings are generally in accordance with the existing literature concerning uterine contractile activity in the healthy uterus. Previously described methods to assess uterine contractility have assessed some subsets of the features that we present (226); however, this is the first study where all the presented features are quantified and evaluated (231). Our novel features for the characterization of different uterine activity and associated patterns - coordination, direction, and velocity - can form a new avenue for research and knowledge into uterine function. Our presented TVUS method for the quantitative analysis of uterine contractions is also easily reproducible (229), quick, objective, and patient-friendly. It is possible to potentially integrate into routine gynaecological practices (after sufficient training), and does not require extensive skill or expertise. The main limitation of the results presented here is the small sample size of the study population. However, we do believe that the presented results are valid due to their general accordance with the currently accepted patterns of uterine peristalsis throughout the menstrual cycle. In addition, most patients received an ultrasound in only one phase of the menstrual cycle for a 4 minute timeframe, and therefore it was not possible to conduct a within-subjects comparison. It can be debated in how far this relatively short recording is representative of the behaviour of the uterus during this phase in general, however a sub-analysis with repeated recordings within subjects was
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