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Received April 2, 2019, accepted May 4, 2020, date of publication June 25, 2020

Maternal-Fetal Simulator 

By L.R. Rodrigo1, A.M. Marcelo2 and A.S. Anderson1  

1 Moinhos de Vento Hospital/ Clinical Engineering, Porto Alegre, Brazil.
2 Moinhos de Vento Hospital/ Clinical and Hospital Engineering, Porto Alegre, Brazil.

ABSTRACT

This study presents the implementation of a low-cost automated prototype, in an open code platform, that simulates the maternal-
fetal signal using the Arduino platform. Several options exist for providing a basic evaluation of the maternal-fetal monitors, but 
the need to simulate the medical environment with a man-machine interface is needed in this age of simulation-based medicine.
Another possible application of this simulator is as a teaching tool. Using data generated by the simulator the man-machine in-
terface can measure fetal movement, uterine activity, and fetal heart rate. The data from the interface can then be compared with 
those presented by the fetal monitor. This comparison makes it possible to check the correct functioning of the equipment tested.

Keywords – Fetal Monitor, Quality Control, Biomedical Simulator, Arduino. 
Copyright © 2021. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY): Creative Commons - Attribu-
tion 4.0 International - CC BY 4.0. The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) 
are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is 
permitted which does not comply with these terms.

INTRODUCTION
The concern over fetal cardiac arrhythmia has in-

creased over the last few years, creating a bigger demand 
in the use of fetal monitoring methods.1 The function of 
the electronic fetal monitor is to detect and record both 
the heart rate of the fetus and the uterine activity of the 
mother in labor.2 To verify the electronic functioning of 
the fetal monitor there is a need for performance testing. 
The tests are divided into two parts – quality evaluation 
(that consists of visual inspection of the structural condi-
tions of the equipment, parts, modules, and accessories) 
and quantity tests (that consists of the measurement or 
simulation of biomedical parameters of the equipment).3

An alternative to the test is to use simulators. Simulators 
aim to present practical situations from everyday life.4 The 
use of simulators also allow new approaches in education 
and medical practices such as simulation-based medicine. 

For example, the students can use anatomical and physi-
ological simulations to predict the results of procedures 
and, therefore, keep up with the results of treatments in 
virtual patients.5 The improvement of simulators in the 
health field is largely due to the use and sophistication 
of Artificial Intelligence-based on microprocessors using 
algorithms that can change concepts and mechanisms 
are used.6

The Arduino platform is an easy to use micro-pro-
cessing tool that allows the utilization of medicine-based 
simulation. Arduino is based on a very versatile system 
microcontroller that potentate its functions beyond 
a simple passive interface of data acquisition and can 
operate independently while controlling many devices.7 

Due to the need for testing of maternal-fetal monitors, 
developing a strict quality process allows for the appraisal 

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Rodrigo, Marcelo and Anderson: Maternal-Fetal Simulator  

INSTALLING THE PERIPHERALS
The system used a selective on/off key. The power to 

the board and peripherals was through a computer source. 
For the electromechanical components (the speaker-
which is responsible for the sound wave emission that 
will stimulate the ultrasonic transducer o the fetal moni-
tor), a TIP122 was used that received power of 12V from 
the switching power supply. Control of simulation of the 
fetal movement was via the use of a 12V relay with a NA 
contact. The pressure sensor used was an MPX5700DP, 
which controlled the pressure inside the neonatal PNI and 
was connected directly in the Arduino platform. The sen-
sor was powered by the 12V source. The pressure bomb 
was connected with the component TIP22 and powered 
by 12V from the switching power supply.

The valve connected to the TIP122 received control of 
the main board and was also powered by the 12V power 
supply. The display was connected to the processor board. 
In this prototype, the Arduino MEGA microcontroller was 
used. The coding platform and free hardware that has its 
own compiler was developed for use by people with little 
programming knowledge.

The microcontroller used in the Arduino MEGA 2560 
was the ATMEL ATmega2560, an 8-bit microcontroller of 
advanced RISC architecture. It has 256 KB of Flash (8 KB 
more are used for the boot-loader), 8 KB of RAM and 4 KB 
of EEPROM. It has 16 MIPS, operating in 16 MHz. Arduino 

based in Atmel ATMEGA, among which can highlight 4 
communication serial channels, 16 analog inputs, and 15 
PWM outings. It has SPI communication, 12C and 6 pins 
of external interruption. The MEGA 2560 board has 54 
input pins and digital outputs that can be used as inputs 
or outputs. The pins operate with a tension of 5V and can 
provide or drain up to 40 mA. Each pin has a “pull-up” 
intern resistor that can be enabled by software. It has 16 
analog inputs (A0 to A15 pins), where the conversion can 
be made with a resolution of 10 bits, that is, the value will 
be converted between 0 and 1023.

IHM
 The IHM of the Arduino platform was chosen so the 

simulator could have mobility and easily interface between 
the operator and the device.

Driver 
The TIP122 was used to control the electromechani-

cal devices.

Power Source
 Standard 12V, 2.3A, real potency of 500 Watts, Effi-

ciency >70%, MTBF of 100.000 hours, 25°C, intern pro-
tection against short circuit OVP/OCP/SCP, AC input with 
manual switching 110/220V, low acoustic noise, cables 
with protection covering, cooling temperature controller 
system, silent ventilator of 120 mm, IEC60950 technical 
norms (electrical safety), IEC 61000 (electromagnetic 
safety), on/off switch.

Diaphragm Pump 
A diaphragm pump was used to inject pressure on 

a plastic membrane controlled by the pressure sensor 
which generated pressures to the touch. Figure 3 shows 
the system functions of the circuit.

Relay – with a NA/NF of 12V.
Speaker – 4Ω/66W.
Neonatal Cuff – Cuff of neonatal PNI with a tube.
Valve – Valve with solenoid of 12V.
Pressure Sensor – MPX5700DP.
TIP122 – 5A, power transducers, 60 volts, 65 watts.

of the level of equipment deterioration. This provides 
information about deficient components and verifies the 
quality of repairs made.8 In the continuous processes of 
improvement, the implementation of quality control aims 
to guarantee the safety and reliability of the results of the 
diagnostic testing.9

Another point to consider is the need to involve the 
assistant medical team in the performance of a hospital’s 
medical technology. Besides understanding the technol-
ogy used, the assistant team (doctors, nurses etc.) will 
need to get involved increasingly in the life cycle of the 
equipment. To help with cost reduction and maximize the 
clinical benefits, interaction with the clinical engineers 
guarantees the effectiveness of preventive maintenance 
through the use of simulator-based tests and allow par-
ticipation in the evaluation of potentially outdated or 
unsafe technology.10 To address this need we developed a 
low-cost automated system prototype to simulate uterine 
contractions and fetal heartbeats. The aim was to make it 
easy to use in universities and hospitals that are looking 
for quality in fetal monitors testing.

METHOD
With the specified, calculated, modeled, and simulated 

data, a prototype was designed, developed, and tested 
according to the flow-gram demonstrated in Figure 1.1

Initially, the project was organized as a study group for 
evaluating the possible solutions for a low-cost prototype 
of a maternal-fetal simulator. Many follow-ups were made 
with the nursing team in the obstetric center to measure a 
real antenatal exam. The other steps outlined in the flow-
gram in Figure 1 are described below in Equation 1 and 
Equation 2 as a two-step conversion calculation that was 
within the limits of the processor and the requirements 
of the maternal-fetal monitor.

Through these calculations Table 1 was created within 
the parameters of the development of the program. Time 
periods with whole numbers were used to facilitate the 
programming.

PROGRAM
 In this step we dealt with programming for the Ar-

duino platform (Figure 2), with the principle of language 
C. Based on Table 1, the periods of each heartbeat were 
defined causing each one to stay for a minute. After this 
step, the signal of fetal movement was programmed with 
the stimulus of five pulses at intervals of one minute. After 
that, the lines of programming were implemented for the 
sensor responsible for controlling the pressure bomb 
causing a variation of pressure of 0–100 mmHg. After 
getting to maximum pressure, to stabilize the circuit for 
a minute at a 50 mmHg, the valve must open to reset the 
pressure of the system. Lastly, the display was programmed 
to show the pulses of fetal movement, uterine pressure, 
and heart rate/frequency of the fetus.

FIGURE 1. Method flow-gram.

TABLE 1. Conversion – Relation between Heart Rate (BPM), 
Frequency (Hz) and Period (Ms)

(BPM) (Hz) Period (Ms)

30,0 0,5 2000,0

60,0 1,0 1000,0

90,0 1,5 666,7

120,0 2,0 500,0

180,0 3,0 333,3

240,0 4,0 250,0

FIGURE 2. Arduino platform circuit diagram.



Rodrigo, Marcelo and Anderson: Maternal-Fetal Simulator 

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Rodrigo, Marcelo and Anderson: Maternal-Fetal Simulator  

PNI, ECG, and electrical tests, in an integrated way by 
adding modules to this simulator. This would be made 
easier due to the simplicity of the program structure and 
that the Arduino platform has many tutorials available 
on the Internet.

CONCLUSION
The goal of simulating uterine contractions and fetal 

heart rate with a low-cost automated system was accom-
plished using quality standards in the tests of the maternal-
fetal monitors and executed by the clinical engineering 
services. Additional improvements, developments, and 
new validations are also achievable.

CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.

REFERENCES

1. Lindsey AD, Robert HA, Sullivan ID, et al. Evaluation of 
fetal arrhythmias by echocardiography. Br Heart J 1983.

2. Zielinsky P. Arritmias cardíacas fetais: papel da eco-
cardiografiapré-natal no diagnóstico e na terapêutica 
intrauterina. In: Cruz FES, Maia IG. Eletrofisiologia 
Clínica e Intervencionista das Arritmias Cardíacas. Rio 
de Janeiro: Ed. Rev. Interna 1997;31723.

RESULTS
After connecting all peripherals, the program was 

run to verify if the simulator was within the minimum of 
uncertainty. To determine the reliability of the prototype 
a digital oscilloscope was connected (Figure 4) in the 
pressure circuit. The cycle of the program was monitored 
through this oscilloscope and calibrated with traceability.

To obtain the final results, the fetal monitor’s transduc-
ers were connected in the simulator and five tests were 
executed with satisfactory results as shown in the IHM, 
with the visualization of the measurement of the fetal 
movement (Figure 5), uterine activity (Figure 6), and fetal 
heart rate (Figure 7).

As a complement to the results, Figure 8 shows the 
system during the testing of the prototype including the 
number identification for the components of the system. 
This is also shown in Figure 8.

DISCUSSION
It wasn’t simple to reproduce the BPM with an electro-

mechanical system and develop a structure that accom-
modates the sensors of many models, to execute a low-cost 
prototype. One of the difficulties was transforming the 
“electronic garbage” (useless components) available into 
the appropriate components needed in the simulator.

One of the improvements to the project could be a Wi-
Fi-connected system to allow Cloud storage of data and 
information collected by the fetal detectors. The data could 
be identified as patrimony or by an identification code.

Proposed future improvement requiring further study 
include the development of similar devices to analyze 

3. Lucatelli MV, Batista MB, Silva HP, Garcia R. Metrologia 
para a Vida Sociedade Brasileira de Metrologia (SBM) 
Setembro 2003;01-05.

4. Dias CF, Rosecler MB, Mussoi RB. Revista Brasileira de 
Informática na Educação 2014;22(2).

5. Villamil MB. Modelagem e Simulação da Articulação 
Temporomandibular. Universidade Federal do Rio 
Grande do Sul. Instituto de Informática. Programa de 
Pós-GraduaçãoemComputação; 2009.

6. Almeida MC, Tavolaro CR, Molisani E. Rev. Bras. Ensino 
Fís.Vol.3n.4.São Paulo 2011;Oct./Dec.

7. Souza AR, Paixão AC, Uzêda DD, et al. A placa Arduino: 
uma opção de baixo custo para experiências de física 
assistidas pelo PC. Revista Brasileira de Ensino de 
Física 2011;33(1)1702.

8. Oliveira LM, Maia JM, Gamba HR, et al. Avaliação da 
qualidade de imagens de equipamentos de ultrassom 
modo-B. Revista Brasileira de Engenharia Biomédica 
2010;26(1):11–24.

9. Severo LS, Lammoglia RS, Saito RH, et al. Aplicação dos 
Testes de Verificação dos Indicadores da Qualidade 
de Equipamentos de Ultra-sonografia. Instituto de 
Eletrotécnica e Energia da USP 2001.

10. Ministério da Saúde. Avaliação tecnológica em saúde: 
subsidiando a melhoria da qualidade e eficiência do SUS 
(Reforsus). Brasília (DF): Ministério da Saúde; 1998.

FIGURE 3. Circuit flow-gram.

FIGURE 4. Frequency generated by Arduino.

FIGURE 5. IHM fetal movement.

FIGURE 6. IHM uterine activity.

FIGURE 7. IHM fetal heart rate.

FIGURE 8. Prototype test.

traceability.To
traceability.To
Fís.Vol.3n.4.São

