Discussion
This study was done to develop a uterine contraction-monitoring tool. A portable device with a smartphone application that pregnant women can use easily was the output of our research. Cost, energy consumption, removing noise and weight were taken into account for more usefulness. This tool is a sample of telemedicine devices that can be used for pregnant women with a high-risk of PTL or for other pregnant women with a physician’s diagnosis. Unlike the Toco device, it is possible to use this product at home in remote areas.
In this device, EHG was used to receive the uterus signals for some reason. The first was that the tocodynamometer must be properly held by a guard to distinguish uterine contractions (24). While using EHG electrodes that are attached to a woman’s skin, avoid the problems of electrode displacement. This means that a pregnant woman can move during the recording signals. Another reason was the power of the device to distinguish between labor contractions and Braxton-Hicks contractions (25). EHG analysis during pregnancy can be used to predict the risk of labor.
The third reason was the evaluation criteria of existing tools. Several studies have calculated the sensitivity, specificity, and predictive values of CTG. Based on most of them, specificity (>90%) was relatively high, but sensitivity (averaging 50%) was low (26). Also, based on Thijsse’s study (27), the accuracy and sensitivity of the EHG are higher than the tocodynamometer. In addition, sensitivity in obese women was 46 to 51% by tocodynamometer and 82 to 97% by EHG. The intrauterine pressure catheter (IUPC) is the more accurate method (27). Especially in obese women, it is more accurate than external tocodynamometry in detecting the power and frequency of uterine contractions (28). However, this method is invasive and has some side effects (29). Nevertheless, Electrohysterography is a non-invasive method to monitor FHR and uterine contractions (12).
The study by Marque et al. (30) has proved that it is possible to detect the risk of PTL as early as the 27th week of pregnancy with a non-invasive method. Other studies (25, 31-33) on pregnant women showed that EHG analysis is a promising and non-invasive diagnostic tool for the diagnosis of PTL.
EHG has some disadvantages. For example, recordings of EHG include some physiological interferences such as abdominal muscle activity, and motion artifacts (34). We used operational amplifiers and filters (low-pass filter, high-pass filter and notch filter) to remove abdominal muscle activity noises.
In the world, multiple home pregnancy monitoring systems have been produced. For example, Bloomlife (35) acquires EHG signals with one channel for capturing uterine contractions (UC). It provides the frequency, pattern, and duration of UC. Invu (36) captures FHR and maternal HR. However, this device does not provide information about UC. Monica Novii wireless patch system (37) captures fetal ECG and UC waveforms in one channel. The device developed in this study was the first device of this type in Iran and can capture UC using EHG signals with three electrodes. In the application, the duration, power and frequency of UC are shown. Also, the application makes an alarm if it detects a contraction other than Braxton Hicks. The facilities in the application are basic. In the future, new features such as an education section for patients, a version of software for nurses and obstetricians, and sending messages to nurses, obstetricians and relatives of pregnant women will be added.