## 1 Introduction  
The intrauterine pressure (IUP) method and the tocogram (TOCO) have been used for uterine contraction monitoring. Both methods present limitations regarding the assessment of uterine contraction properties and characteristics [1; 2; 3]. The gold standard for measuring the uterine pressure is the IUP, which provides the best information concerning uterine contractions since it is based on a pressure sensor inserted in the amniotic space. The IUP is not a routine pregnancy monitoring procedure, considering that it can only be used after membrane rupturing. As a consequence, it is mainly used in selected cases, such as when the subject is obese or is already in labor [4; 5]. On the other hand, the TOCO technique, based on a strain gauge, is widely used in pregnancy and labor monitoring. The method remains unchanged since the late 1960's. The TOCO presents a mismatch between amplitude and the strength of the uterine contraction, which leads to decreased predictive value. The TOCO acquisition also poses a problem for subjects with body mass index (BMI) higher than 30 [2]. The technique, which is often used as a uterine contraction frequency meter, is not considered an adequate methodology for routine preterm risk evaluation. The electrohysterogram (EHG) is an alternative to the TOCO and IUP methods, and it is obtained noninvasively through electrodes placed on the abdominal surface [6; 7; 8; 9]. The EHG has been considered an appropriate tool for long-term pregnancy and childbirth monitoring due to its non-invasive nature. Besides, it is easily obtained and can be used as early as the 20 th week of gestation. Although the BMI has been reported as having an imperceptible impact on the EHG, one of its main advantages [10; 11], another study [12] reports a fat-induced low-pass filtering effect. The EHG is a signal with increased complexity that often requires the application of advanced signal processing analysis techniques. There are no standards regarding electrode location, acquisition system, or feature analysis parameters [5; 13; 14]. Research in this field has grown with the introduction of more powerful algorithms enabled by the ever-increasing platforms' computational power. Uterine contractions are present from as early as 20 weeks of gestational age, and they may be detected through maternal perception, TOCO, or EHG. These early pregnancy contractions may have low mechanical impact due to the poorly coordinated uterine cell-to-cell communications, and therefore may be missing in the TOCO and present in the EHG. They are ineffective as far as labor is concerned, but can convey important information in the context of preterm risk evaluation or generally for pregnancy monitoring [15; 16; 17; 18]. As labor approaches, a preparatory process takes place in the uterine muscle, where an increase of cell-to-cell coupling is present [16; 17; 18]. This translates into more expressive contraction levels due to the synchronicity arising from the structural and functional cell coupling alterations [19]. It stands out that uterine contractions detected through the EHG commonly present an associated energy burst. These energy bursts above the basal activity are used herein as a contraction detector feature. Several studies have been performed with different contraction detection methodologies in the EHG signal. [PERSON] et al. [20] used neural networks and wavelet analysis to perform contraction detection and classification for four event classes: Alvarez, Contractions, Foetal Movements and LDBF (_Longue Duree Basse Frequence_) [21], with an overall accuracy of 80%. [PERSON] et al. [22] used a low-pass filter and a root mean square (RMS) computation over a 60 s window to track uterine contractions in the EHG. In this study, 87% of EHG contractions and 96% of the relative TOCO events were regarded as consistent. The same authors [23] outlined the importance of spectral analysis in the development of the EHG research. [PERSON] [24] investigated the best wavelet packet tree for EHG components detection.