Measurement and Validation of Fetal Heart and Fetal Movement Signals Detected Via Non-adhesive Sensors
Phase: NA
Conditions: Fetal Distress With Antenatal Problem, Fetal Growth Retardation
Sponsor: University of Manchester

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RESEARCH PROTOCOL 
 
 
 
 
 
 
 
Measurement and Validation of Fetal Heart and Fetal Movement Signals 
Detected via Non-adhesive Sensors 
 
 

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Contents 
 
 
1) 
RESEARCH TEAM & KEY CONTACTS 
3 
2) 
INTRODUCTION 
4 
3) 
BACKGROUND 
4 
4) 
STUDY OBJECTIVES 
5 
5) 
STUDY DESIGN & PROTOCOL 
6 
6) 
STUDY PARTICIPANTS 
7 
7) 
OUTCOME MEASURES 
8 
8) 
DATA COLLECTION, SOURCE DATA AND CONFIDENTIALITY 
9 
9) 
STATISTICAL CONSIDERATIONS 
10 
10) DATA MONITORING AND QUALITY ASSURANCE 
11 
11) ETHICAL CONSIDERATIONS 
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12) STATEMENT OF INDEMNITY 
12 
13) FUNDING 
12 
14) PUBLICATION POLICY 
13 
15) REFERENCES 
13 
 
 
 
 

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1) RESEARCH TEAM & KEY CONTACTS  
Chief Investigator: 
 
Name:  Professor Alexander Heazell 
 
Address:  
Maternal and Fetal Health Research Centre 
5th Floor Research, St. Mary’s Hospital 
Oxford Road, Manchester 
M13 9WL 
  
Email: alexander.heazell@manchester.ac.uk 
 
Telephone: (0161) 276 6484 
 
Signed: 
 
24/05/2022 
Co-investigator(s): 
 
Name: Dr Jayawan Wijekoon  
 
Address:  
D31b Sackville Street Building,  
Sackville Street, 
Manchester,  
M1 3BU  
 
Email: 
jayawan.wijekoon@manchester.ac.uk 
 
Telephone 0161 306 4736 
 
Fax 0161 306 8946  
Co-investigator(s): 
 
Name: Dr Anura Fernando 
 
Address:  
Department of Materials, University of Manchester, 
A35B1, Sackville Street Building,  
M1 3BU 
 
Email: anura.fernando-2@manchester.ac.uk 
 
Telephone: 0161 306 3753 
 
Fax: 
 

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Sponsor(s): 
 
Name: The University of Manchester  
 
Sponsor contact: Mr Mohammed Zubair, Research 
Governance, Ethics and Integrity Manager 
 
Address:  
2nd Floor, Christie Building, Burlington Street, 
Manchester, M13 9PL 
 
Email: mohammed.zubair@manchester.ac.uk 
 
Telephone: 0161 275 2725 
Lead R&D Trust contact(s): 
 
Name: Manchester University NHS 
Foundation Trust 
 
Contact: Dr Elizabeth Mainwaring 
 
Address:   
Manchester University NHS Foundation 
Trust 
Research Office,  
Manchester University NHS Foundation 
Trust 
29 Grafton Street, Manchester, M13 
9WU 
 
Email: R&D.applications@mft.nhs.uk 
 
Telephone: 0161 276 3340 
2) INTRODUCTION 
A multidisciplinary team of a doctor and engineers have developed a new sensor that will be able 
to detect mothers’ and babies’ heartbeat and babies movements in late pregnancy. This sensor can 
be placed in contact with the mothers’ skin over the pregnant uterus without having to be stuck 
down. We anticipate that this sensor would allow us to monitor babies for longer periods of time 
which might help us to better identify babies who are being deprived of oxygen during pregnancy. 
We need to test these sensors on women in late pregnancy for two reasons. Firstly, we need to 
ensure they reliably measure mother and babies heart rates without interference from movement 
or other electrical equipment. Secondly we need to ensure that the information they provide is 
accurate (compared to current measurement techniques).  
We will carry out a study in two phases. The first phase will include up to 24 women to develop the 
sensors to ensure that they can obtain consistent signals from mothers' and babies' heartbeats 
without interference from movement and other electronic devices. We will adjust the electronics in 
the sensors to ensure they give the best signal. The second phase will include up to 45 women to 
see whether the information detected by the sensors is comparable to existing technologies. This 
information will help us to see whether these sensors can be organised into a new device for fetal 
monitoring which can then be tested. 
3) BACKGROUND 
Current technologies to objectively assess fetal wellbeing including fetal movement counting using 
“kick charts” and intermittent cardiotocography have little or no effect on reducing perinatal 

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mortality, even in high-risk populations.1-3 Despite this, they are commonly used in clinical practice, 
particularly for pregnancies at high-risk of adverse pregnancy outcome. One reason for the use of 
these technologies is that there are no more effective alternatives. There is limited evidence that 
computerised analysis of the fetal heart rate trace, in high-risk pregnancies, is associated with a 
reduction in stillbirth.3 This suggests that computerised analysis can detect abnormalities which are 
not detected by visual analysis of the heart rate trace.  
 
One suggestion to improve the technologies is to increase the period of monitoring, or even develop 
an approach which can continuously assess fetal wellbeing.4 This has led to the development of 
various devices to objectively measure fetal activity or fetal heart rate. However, none of these 
devices have been adopted into clinical practice. The plethora of potential devices suggests that the 
concept is popular but that a practical, reliable and acceptable device has not yet been developed. 
We have demonstrated that professionals would be willing to use continuous monitoring, especially 
in mothers at high-risk of complications, although they had concerns about the practicality of the 
approach and of causing maternal anxiety.5 Using one device which has been developed to market 
(MONICA AN24) we demonstrated that women were willing to use a device to monitor the fetal 
heart rate for extended periods but that some physical aspects of the device, specifically the 
adhesive electrodes and wires led to concerns from women that they may disconnect or damage 
the device.6,7 There was also evidence of significant periods where the fetal heart rate signal was 
lost amounting to 31% of each trace on average.7 This suggests that improvements in sensors to 
detect fetal heart rate are needed. 
 
Working together with researchers in the School of Engineering (Departments of Electronic 
Engineering and Textiles) we have developed non-adhesive capacitively-coupled sensors which can 
detect signals of the magnitude of the fetal heart rate which is approximately 100 times weaker 
than an adult heart rate. It is envisaged that these non-adhesive sensors would be arranged in an 
array to detect the fetal heart rate irrespective of the position of the fetus. Before we can develop 
a device we need to ensure that these sensors can consistently and reliably detect the mother's and 
baby's heart rate. 
4) STUDY OBJECTIVES  
4.1 Primary Question/Objective: 
The primary aim of this project is to conduct initial studies using non-adhesive sensors to determine 
whether they are able to consistently detect the mother's and baby's heart rate and whether this 
can be distinguished from background electrical noise.  
4.2 Secondary Question/Objective: 
This project will determine whether placing these sensors in an array (a group) provides better 
detection of the mother's and baby's fetal heart rate and movements. 

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This project will determine whether the electronic signals detected can reliably detect mother's and 
baby's heart rates when compared to currently established methods. 
This project will determine women’s experiences of having the sensors applied to their abdomen 
and the concept of longer-term fetal monitoring. 
5) STUDY DESIGN & PROTOCOL 
5.1 Participants 
We will conduct a cohort study of women with a healthy singleton pregnancy over 28 weeks’ 
gestation.  
5.2 Study Intervention and/or Procedures 
In the first part of the study we will ask up to 24 pregnant women to wear the device and determine 
whether the device consistently detects the electronic signals and to reduce recording of 
background electrical noise e.g. from electrical wires / devices / sockets etc. which are likely to emit 
electrical activity in the same microvolt range as the fetal heart rate trace. 
 
In the first part of the study participants will be from three separate time periods in late pregnancy 
(8 women in each time frame) 28weeks +0 days - 31weeks +6 days (usually written as 31+6) , 32+0-
35+6 weeks and finally from 36+0 until 40+0 weeks. Women will be recruited from the Tommy’s 
research clinics and the antenatal clinics at St Mary’s Hospital, Manchester. All participants will have 
an ultrasound scan prior to participation to measure baby's size, the liquor volume and umbilical 
artery Doppler (if not already performed in the preceding 7 days). This will ensure that baby is well 
before the sensors are used. We will measure the electrical activity of the participants skin and soft 
tissues using an electrodermal activity meter which uses two adhesive electrodes attached to the 
maternal abdomen. If needed, we will make adaptations to the electronics to optimise the detection 
of the mother's and baby's heart rate. All participants will give written informed consent before any 
experimental activities commence. 
 
Participants will be asked to lie on an examination couch for up to 60 minutes at 45 degrees while 
the electronic sensor(s) are held in contact with the maternal abdomen by an elastic garment (A 
typical array of sensors is shown in Appendix A) with or without conductive gel applied. If 
participants are uncomfortable they will be able to sit or stand to relieve their discomfort. Basic 
information including body mass index, stage of pregnancy and estimated fetal weight will be 
recorded on a proforma. Participant comfort or discomfort during the period of monitoring will be 
assessed by non-participant observation during the monitoring session. These observations will be 
undertaken by a MSc student who is a registered midwife. 
 
If consistent signals can be obtained we will assess whether the sensors can accurately display 
maternal heart rate and fetal heart rate at different stages of late pregnancy. To assess whether the 
recording is accurate we will compare the output from the sensors with current methods to assess 

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maternal heart rate (ECG), fetal heart rate (traditional CTG and MONICA24). We will use ultrasound 
scan to assess whether fetal movements are associated with expected changes in fetal heart activity. 
 
In the second phase of the study, to assess sensor reliability we will recruit up to 15 women from 
each gestational age group from 28+0-31+6 weeks, 32+0-35+6 weeks and finally from 36+0 until 
40+0 weeks. Women will be approached if they have healthy singleton pregnancies and have a pre-
pregnancy BMI from 20-35. As previously, women will be recruited from the Tommy’s research 
clinics and the antenatal clinics at St Mary’s Hospital, Manchester. All participants will have an 
ultrasound scan prior to participation to measure baby's size, the liquor volume and umbilical artery 
Doppler (if not already performed in the preceding 7 days). This will ensure that baby is well before 
the sensors are used. We will measure the electrical activity of the participants skin and soft tissues 
using an electrodermal activity meter which uses two adhesive electrodes attached to the maternal 
abdomen. The correlation between the maternal and fetal heart rates obtained using established 
techniques and the new sensors will be calculated.  
 
Participants will be asked to complete a short baseline questionnaire before commencing the 
monitoring process, a saliva sample will then be collected for cortisol analysis. Participants will be 
asked to lie on an examination couch for up to 60 minutes at 45 degrees while the electronic 
sensor(s) are gently held in contact with the maternal abdomen by an elastic belt. In addition to the 
new sensors the fetal and maternal heart rate will be recorded using the MONICA AN24 device and 
fetal movements will be recorded with ultrasound (for 20 minutes of the 60). If participants are 
uncomfortable they will be able to sit or stand to relieve their discomfort. Participant comfort or 
discomfort during the period of monitoring will be assessed by non-participant observation during 
the monitoring session. These observations will be undertaken by a MSc student who is a registered 
midwife. Basic information including body mass index, stage of pregnancy and estimated fetal 
weight will be recorded on a proforma (see Appendix B). In addition, participants will be asked to 
complete a questionnaire about anxiety and wearing the device after the monitoring process (see 
Appendix C). At this point, a further saliva sample will be collected for a comparative cortisol 
measurement. 
Participants who agree to have an interview about their experience of wearing the sensor to monitor 
their baby’s heart rate pattern will be interviewed by the Lydia Hughes (Masters student / midwife). 
This interview will follow a semi-structured interview guide (see Appendix B). The interview will be 
conducted prior to the participant leaving the hospital. The interview will be audio-recorded and 
transcribed verbatim. Once the transcription has been checked against the audio recording for 
validity the audio recording will be deleted; data will be stored on a password protected hard drive 
to prevent the risk of third-party access. Data will only be utilised for the purpose of the study and 
will be disposed of upon completion. To ensure the wellbeing of the participants, a distress protocol 
has been devised and will be activated where necessary (Appendix C).  
6) STUDY PARTICIPANTS 
6.1 Inclusion Criteria: 
Commented [AH1]: This will need to be added.  

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Participants will be included if they have a non-anomalous singleton pregnancy after 28 weeks' 
gestation with an estimated fetal weight >10th centile < 90th centile. Participants will be 16 years 
or over in order that they can give independent consent.  
6.2 Exclusion Criteria: 
Participants will be excluded if there are fetal anomalies (as defined by the NHS Fetal Anomaly 
Screening 
Programme 
- 
https://www.gov.uk/guidance/fetal-anomaly-screening-programme-
overview), it is a multiple pregnancy, there is evidence of Fetal Growth Restriction (Estimated Fetal 
Weight <10th centile) or if participants cannot speak or do not understand fluent English. 
Participants will not be able to participate if they are unable to give informed consent. Participants 
<16 years of age will be excluded from this study.  
6.3 Recruitment:  
Eligible pregnant women will be identified in the research and antenatal clinics through the routine 
work of the clinical staff. Only members of the clinical care team will have access to any identifiable 
data prior to consent. In addition, we will display recruitment posters so that potential participants 
will know that the study is being undertaken in the clinical area. 
 
If potential participants agree, a research midwife or CI will discuss the study with them and provide 
a participant information sheet and will be asked to complete a consent to contact form. 
Participants will have at least 24 hours to decide whether or not to participate in the research. If 
they agree to participate, then an appointment will be made for them to attend the Maternal and 
Fetal Health Research Centre to undertake the study. Written consent will be taken prior to 
participating in the study recorded on the specified form. 
6.5 Participants who withdraw consent [or lose capacity to consent]:  
Participants can withdraw consent at any time without giving any reason, as participation in the 
research is voluntary, without their care or legal rights being affected. For participants who 
voluntarily withdraw from the study who have previously consented to the study data up to the 
time of withdrawal will be included in the study unless the participants specifically request for all of 
their data be removed.  
As participation in the study is limited to a single window during which participants will have a period 
of monitoring capacity to consent will be continuously monitored. After this period of contact 
ongoing capacity will not be assessed and participants’ data will be included in the study unless 
participants specifically request for their data to be removed. 
7) OUTCOME MEASURES 
At this stage this study is primarily of academic interest. These studies will determine whether the 
non-adhesive electrodes can detect signals from the fetal heart rate and fetal movements and 
distinguish this from background noise and the maternal heart rate.  

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These studies will demonstrate whether the sensors are comfortable and what women’s 
experiences are of the monitoring procedure. 
Upon completion of the study we will know if these sensors can reliably detect maternal and fetal 
heart rate and changes associated with fetal movement. We will also know whether an array of 
sensors performs better than a single sensor alone. We will know whether women find the 
monitoring process comfortable and acceptable. 
8) DATA COLLECTION, SOURCE DATA AND CONFIDENTIALITY 
Data will be obtained from the medical case records by the research staff. The data will initially be 
recorded on a paper case report form. These data will then be transferred to a secure electronic 
database held on the University of Manchester online storage. The only personal data to be 
collected is the hospital unit number and participant initials to allow traceability of medical records. 
These will be stored in a separate password protected computer file from the study data linked only 
by a participant number. Non-identifiable data will be stored on University Computers. All 
computers will be password protected and encrypted according to University of Manchester policy. 
We will not store personal identifiable information with study data. Information will be coded by 
participant study number. Participants will not be identifiable from the stored data set itself. 
If they agree to participate in the interview after the monitoring period this will be audio-recorded 
and transcribed. Once the transcription has been checked against the audio recording for accuracy 
the original recording will be deleted. The transcription will be identified by their study number. 
Each participant will be assigned a study number, this will be linked to the consent form only. 
Personal identifiable data, including consent forms, will be stored in a locked filing cabinet in the 
Maternal Fetal Health Research Centre. 
Storage of personal identifying data will only be accessible to research staff directly involved in this 
project in line with GCP guidelines and will only be stored on NHS computers. Electronic data will be 
linked using the study number; no personal identifiable data will be stored on the electronic 
research database. Any laptops used will be password protected and will contain no identifiable 
participant data. 
To maintain confidentiality computer records specific to the research outcomes will use the 
participant's study number to identify them (this study number will be listed on the consent form, 
allowing linkage back to the individual). Personal data will remain confidential within the research 
team. Confidentiality procedures in line with University of Manchester Research Governance 
guidelines and NHS Code of Confidentiality will be adhered to at all times. If direct quotations are 
published from questionnaires the confidentiality of all participants will be maintained with the use 
of pseudonyms. 
The research team will have access to personal data. Study data and material may be looked at by 
individuals from the University of Manchester, from regulatory authorities or from the NHS Trust, 
for monitoring and auditing purposes, and this may well include access to personal information. 

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Consent forms will be retained as essential study documents. Personal data from the pseudo-
anonymised database will be deleted as soon as the study dataset is complete (anticipated to be 18 
months from commencing the study) and no further validation is required from clinical records. The 
anonymised data will be stored for 10 years in line with regulatory requirements. 
The data generated by the study will be analysed by the study team comprising Lydia Hughes 
(Masters Student), Lisen Zhu (PhD student), Prof Alexander Heazell, Dr Jayawan Wijekoon and Dr 
Anura Fernando. The Chief Investigator will be the custodian of the data for the study. 
9) STATISTICAL CONSIDERATIONS 
9.1 Statistical Analysis 
All data collection and analysis will take place simultaneously and will be analysed by the research 
team. In the first phase of the study we will be recording the presence of maternal and fetal 
electrocardiogram recordings and any interference from movement / other electrical sources. In the 
second phase of the study we will analyse the agreement between signals obtained via the novel 
sensors and information obtained from established methods (ultrasound, MONICA AN24 device) 
using correlation.  
9.2 Qualitative Analysis 
Thematic analysis will be used Braun & Clarke’s six-step thematic analysis framework will be used 
(Appendix D) to analyse the interview data as it is appropriate for this form of qualitative data by 
providing a flexible yet structured framework to explore participants’ experiences, uncovering 
themes and patterns. It will highlight diverse perspectives to ensure that all voices are represented, 
which is integral in health-care research. Initial themes will be derived by the Masters student and 
discussed with the wider research team. 
9.3 Sample Size: 
A sample size calculation could not be performed. We have consulted with other researchers with 
expertise in medical devices who suggested that up to 24 women would be sufficient to ensure that 
signals could be consistently obtained and allow changes to the device. To test reliability greater 
numbers are required as the stage of pregnancy and other factors (mother/baby size) may have an 
effect. We plan to continuously analyse our data, if we achieve our objectives before the planned 
number of participants are recruited we will not continue to recruit. 
The proposed sample size for the qualitative data is 15. During interviews and observations, the 
researcher wishes to reach a point of data saturation whereby no new themes are emerging, a 
typical sample size for qualitative data is 5-30 depending on the nature and complexity; 12 
participants is suggested as sufficient to understand the lived experiences of individuals in depth. 
Commented [AH2]: This will need to be added 

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10) DATA MONITORING AND QUALITY ASSURANCE 
The study will be subject to the audit and monitoring regime of the University of Manchester. The 
investigators / institutions will facilitate study-related monitoring, audits, review by independent 
ethics committee and regulatory inspections providing direct access to source data / documents to 
authorised study or regulatory personnel. 
11) SAFETY CONSIDERATIONS AND ADVERSE EVENTS 
As this is a preliminary study to assess whether sensors can detect maternal and fetal heart rate 
there are likely no safety implications for participants. However, if examination of the maternal or 
fetal heart rate identified a problem during the experimental protocol the procedure would be 
stopped and the mother transferred to a left-lateral position to allow a period for the abnormal 
observations to resolve. The mother would be clinically assessed by the research midwife, if the 
abnormal observations do not resolve the mother would be transferred to the maternity 
department at St Mary’s Hospital for further management. A handover would be given to the clinical 
staff by the research midwife looking after the participant. The need to terminate the protocol 
would be recorded in the study and reported in the final analysis. 
We will stop the study earlier if we achieve our outcomes before completing our recruitment 
targets. 
12) PEER REVIEW 
This study has been peer-reviewed as part of the Maternal and Fetal Health Research Centre annual 
peer review from Tommy's. The funding for the project has been continued following a favourable 
peer review although we have not been given specific comments. Additional independent external 
review has been obtained from Prof Fiona Dennison from the University of Edinburgh. 
13) ETHICAL and REGULATORY CONSIDERATIONS  
13.1 
Approvals  
Health Research Authority approval will be obtained before commencing research processes. The 
Medicines and Health Regulatory Agency (MHRA) have confirmed that as this study is for academic 
interest only, approval from the MHRA is not required. The study will be conducted in full 
conformance with all relevant legal requirements and the principles of the Declaration of Helsinki, 
Good Clinical Practice (GCP) and the UK Policy Framework for Health and Social Care Research 2017. 
 
 

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13.2 
Risks 
 
As with any study maintaining confidentiality is an important consideration and measures will be 
put in place to ensure this. For example, all paper confidential information will be stored securely in 
a locked filing drawer in the Maternal & Fetal Health Research Centre and will only be accessible to 
members of the research team. All electronic information will use trial identification numbers and 
will be stored on a secure computer.  
 
Participants may also be concerned that the views they express during the study may affect their 
rapport with their care givers. All pregnant participants will be reassured that this will not happen 
as the questionnaires will be administered by a research midwife who is not involved in delivering 
patient care, nor will divulge participants' views to staff members. Potential participants may feel 
under pressure to participate. Participants will be assured that participation / non-participation will 
not affect their care. 
 
There is a risk that women receiving monitoring with new sensors may believe that they are 
receiving additional monitoring of their baby and therefore do not need to be aware of normal signs 
of pregnancy compromise. Due to this risk all women would be made aware that the purpose of the 
study is to assess the ability of these new sensors to detect mother and baby's heart rates. This 
information will be available in the participant information sheet, the consent form and will be 
subsequently reiterated prior to written consent and use of the sensors. 
 
If any participant discloses something which raises serious concerns about the safety of themselves 
or others, it may be necessary to break confidentiality and inform relevant parties. If the issue was 
regarding the safety of a child or vulnerable adult the Manchester University Foundation NHS Trust's 
child protection and adult safeguarding policies would be followed.  
 
There are no risks to the researchers. 
14)    STATEMENT OF INDEMNITY 
The University has insurance available in respect of research involving human subjects that provides 
cover for legal liabilities arising from its actions or those of its staff or supervised students.  The 
University also has insurance available that provides compensation for non-negligent harm to 
research subjects occasioned in circumstances that are under the control of the University. 
15)    FUNDING and RESOURCES 
This study is funded by Tommy’s and internal funding from the University of Manchester from the 
Engineering and Physical Sciences Research Council (EPSRC). 

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16)    PUBLICATION POLICY 
The investigators will disseminate the results of this study at appropriate national and international 
scientific meetings such as the British Maternal Fetal Medicine Society. The findings will be included 
in a Masters Thesis submitted by Ewa Matthews and a PhD thesis submitted by Mr Mhd Anas 
Alsakkel. No personal identifiable information will be included in the dissemination of study findings.  
Primary responsibility for preparing publications will lie with the Chief Investigator, Prof Alexander 
Heazell. To safeguard the integrity of the study, data from the study will not be presented in public 
before the main results are published without the prior consent of the co-investigators. 
Acknowledgements will include the trial staff at the study site. 
Participants will not be informed of the results directly as this would require storing personal 
information (address/email address) for an extended period. We will publish a summary on our new 
departmental website (currently under development) and will signpost participants to that. 
17)    REFERENCES 
1. 
Alfirevic Z, Stampalija T, Gyte GM. Fetal and umbilical Doppler ultrasound in normal 
pregnancy. Cochrane Database Syst Rev 2010; (8): CD001450. 
2. 
Alfirevic Z, Stampalija T, Gyte GM. Fetal and umbilical Doppler ultrasound in high-risk 
pregnancies. Cochrane Database Syst Rev 2010; (1): CD007529. 
3. 
Grivell RM, Alfirevic Z, Gyte GM, Devane D. Antenatal cardiotocography for fetal 
assessment. Cochrane Database Syst Rev 2012; (1): CD007863. 
4. 
Brown R, Wijekoon JH, Fernando A, Johnstone ED, Heazell AE. Continuous objective 
recording of fetal heart rate and fetal movements could reliably identify fetal compromise, which 
could reduce stillbirth rates by facilitating timely management. Medical hypotheses 2014; 83(3): 
410-7. 
5. 
Brown R, Johnstone ED, Heazell AE. Professionals' views of fetal-monitoring support the 
development of devices to provide objective longer-term assessment of fetal wellbeing. J Matern 
Fetal Neonatal Med 2016; 29(10): 1680-6. 
6. 
Crawford A, Hayes D, Johnstone ED, Heazell AEP. Women's experiences of continuous fetal 
monitoring - a mixed-methods systematic review. Acta Obstet Gynecol Scand 2017; 96(12): 1404-
13. 
7. 
Crawford A, Anyadi P, Stephens L, et al. A mixed-methods evaluation of continuous 
electronic fetal monitoring for an extended period. Acta Obstet Gynecol Scand 2018; 97(12): 1515-
23. 
 
 
 

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Appendix A 
The diagram in Figure 1 shows illustration of a typical planned sensor array design. 
 
Figure 1. Sketch of potential sensor array configuration for fetal heart monitoring 
An array of sensors similar to the one presented in Figure 1 will be held onto a pregnant woman’s 
abdomen by means of an elasticated vest such as the one shown in Figure 2: 
 
Figure 2. Demonstration 0f an ECG sensor arrangement. 

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Electrical safety 
The only intended active element of the array is the reference electrode commonly known as the 
“right leg driver”. The body, acting as an antenna, picks up electrical environmental noise (primarily 
at 50Hz) that interferes with electropotentials picked up at the skins surface. The driven right leg 
actively cancels this interference. This driver is connected to a patient via a 100 k resistor. The 
other electrodes are capacitively coupled to their respective amplifiers, the d.c. current flowing 
under no-fault will be much lower than the “right leg driver” electrode. 
For the “right leg driver”, with the op-amp power supply voltage set at 5V, in the no-fault condition, 
the limit is 10 A (American Standard). The maximum current that could flow from the amplifier 
into the body in a single fault condition is less than the regulatory limit of 50A [1] (for example, a 
fault might constitute the grounding of another electrode). [This limit increases to 5mA at 100kHz].  
These current limit conditions require that the equipment is isolated from the patient.  
Driven right leg circuits [2] have been in common usage within ECG equipment for a number of 
years.  
Electrical Isolation 
All testing on pregnant women will be carried out with the monitoring laptop PC using battery 
power, so as to ensure that any equipment fault will not result in electric shock at mains voltage. 
We will attached the laptop computer to a monitor that will be mains powered. Additional signal 
and power line isolation is provided between laptop and the patient mount ECG equipment – It 
avoids excessive electrical noise coupling, but also adds another layer to patient safety. 
References for Appendix A 
1. “Safe current limits for electromedical apparatus”. ANSI/AAMI ES1-1993. See Table 1. 
2. “Driven-right-leg circuit design”. Winter, B.B. and Webster, J.G., 1983. IEEE Transactions 
on Biomedical Engineering, (1), pp.62-66.