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.