Today, many of the characteristics of the transabdominal uterine electromyogram (EMG) are well established. Some of these characteristics are currently used to monitor pregnancy and detect labor. However, further investigations are needed in order to improve true labor detection. We investigated in this study the way the energy distribution of the uterine EMG signal is modified during pregnancy and in labor. We analyzed recordings of uterine electrical activity in eleven women at different increasing pregnancy terms and at labor. We introduced a method for pregnancy monitoring based on the evolution of the energydistribution of the uterine EMG throughout gestation using wavelet packet transform (WPT). The results obtained from the analyzed data indicate that energy emerges significantly towards higher frequencies along gestation. Furthermore, we observed a noticeable difference in the energy distribution between two studied classes (pregnancy and labor). The results are supported by statistical analysis using t-test indicating good statistical significance with a confidence level of 95%. Our study provides convincing evidence that pregnancy can be monitored and labor can be detected by the means of uterine EMG using its energydistribution. Therefore, the analysis of uterine electrical activity can be very promising to identify preterm labor.