## 4 Discussion  
In this paper, we test the hypothesis that the proposed EUG can be used for monitoring the uterine contractility across the menstrual cycle by measuring the electrical activity of the JZE in healthy, porous, nonpregnant women. To summarize, waveforms closer to the fundus were processed. The RMS Voltage Amplitude (VJZE-RMS) (in \(\upmu\)V) and the Mean Frequency (f)ZE-mean) (in cycles/min) of the JZE's electrical activity, as direct indicators of the intensity and frequency changes in the JZE's contractions, were extracted from the recorded waveforms. There was a trend in the median values of the VJZE-RMS decreasing from the EP to the LP phase. During the EL phase, an upward trend was observed, reaching its highest value during the LL phase when compared to the LP phase. The fJZE-mean showed the opposite trend, increasing from the EP to the LP phase. During the EL phase, a downward trend was observed, which continued to fall in the LL phase, when compared to the previous three phases. In a nongravid uterus, the innermost layer of the myometrium, the JZE, is the main source of peristaltic activity across the menstrual cycle. The endometrial stem/progenitor cells lie in the basalis layer of the endometrium next to the myometrium and the junctional zone. Myometrial cells are niche cells, regulating the activities of endometrial mesenchymal stem-like cells (eMSCs) with self-renewal activity, influenced by cyclic estrogens and progesterone secretion [14]. The uterus derives its innervation from the lumbar plexus. Figure 4: A qualitative representation comparing the measured electrical activity using the EUG in (**a**) Frequency and (**b**) RMS Voltage Amplitude and the change in hormonal levels across the menstrual cycle. The lumbar plexus is formed from the nerve roots L1-L4 and gives rise to the iliohypogastric, ilioinguil, genitofemoral, femoral, and obturator nerves. As such, these nerves are important to consider when describing the contractility, the neurophysiology, and possibly the pain pathology of the uterus [15]. Previous studies have determined that the endometrial waves are initiated in the sub-endometrial myometrium, but the link between the innervation of the uterus and this contractility mechanism is still not clear [16; 17]. The estrogens affect the central nervous system and, together with progesterone, play a role in neurotransmission and act as neuromodulators in the uterus. The estrogens accelerate the uterine contractility, while the progesterone decreases the uterine contractility, creating a quiescent state for assisting successful embryo placement [16; 18]. Based on the anatomy and neurophysiology described, the placement position of the EUG was important, as it enabled the capture of the most representative signals. By only having a few single layers of cells between the electrode and the JZE, the signals were interpreted as contractions with an origin in the JZE, confirming its ability to assist in the monitoring of the contractive uterus. Future research could subsequently focus on the EUG's ability to assist in decision making in, for instance, monitoring the optimal day for embryo transfer and/or assisting in personalized hormonal treatments during IVF. In porous, healthy women with normal uterine and ovarian sonographic characteristics, the fJZE-mean showed statistically significant lower values for the LL phase, compared to the other three phases of the menstrual cycle. The fJZE-mean measures the frequency content of the JZE's electrical activity, which is closely related to the uterine contractility. The results agree with the previously observed contractility trends of [PERSON] et al. (2000), who successfully demonstrated the emphasis on the hormonal dependence in uterine contractility [8]. The EUG also successfully distinguished the different phases of the menstrual cycle that were associated with the JZE's contractility.