Impact of face mask use during the non-stress test in pregnancy

Abstract

Introduction and aim. Face masks used to protect against the COVID 19 pandemic have become a daily routine. The aim of this study was to examine the possible effects of mask use on non-stress test (NST) results during pregnancy. Material and methods. A total of 951 pregnant women were included in the study. They were divided into two groups as those who wear masks and those who do not. These pregnant women were also divided into subgroups as preterm and term periods. Results. The mean age of the pregnant women was 31.2±4.9 and their gestational weeks were between 34+0 and 40+6. There was no significant difference between 34 and 37 gestational weeks pregnants in terms of FHR, reactivity, non-reactivity, deceleration, FHR category distribution and number of fetal movements (p>0.05). The variability was significantly higher in those who did not wear a mask (p<0.05). In pregnancies >37 gestational weeks there was no significant difference in terms of FHR, reactivity, non-reactivity, variability, deceleration and FHR category distribution (p>0.05). The number of fetal movements was significantly (p<0.05) lower in the mask-wearing group. Conclusion. Mask use should be considered in NSTs where variability is reduced or fetal movements are low. Thus, misinterpretation of the NST can be avoided.

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114 European Journal of Clinical and Experimental Medicine 2023; 21 (1): 114–119
This article is an open access article distributed under the terms andconditions of the Creative Commons Attribution (CC BY 4.0) license.
http://www.ejcem.ur.edu.pl
European Journal of Clinical and Experimental Medicine
Eur J Clin Exp Med 2023; 21 (1): 114–119
Impact of face mask use during the non-stress test in pregnancy
Ali Gursoy 1, Ezgi Dogan Tekbas 2
1 Department of Obstetrics and Gynecology, Faculty of Medicine, Maltepe University, Turkey
2 The Gynecological Clinic of Hospital-Holweide, Cologne, Germany
ABSTRACT
Introduction and aim. Face masks used to protect against the COVID 19 pandemic have become a daily routine. The aim of this
study was to examine the possible eects of mask use on non-stress test (NST) results during pregnancy.
Material and methods. A total of 951 pregnant women were included in the study. They were divided into two groups as those
who wear masks and those who do not. These pregnant women were also divided into subgroups as preterm and term periods.
Results. The mean age of the pregnant women was 31.2±4.9 and their gestational weeks were between 34+0 and 40+6. There
was no signicant dierence between 34 and 37 gestational weeks pregnants in terms of FHR, reactivity, non-reactivity, decel-
eration, FHR category distribution and number of fetal movements (p>0.05). The variability was signicantly higher in those
who did not wear a mask (p<0.05). In pregnancies >37 gestational weeks there was no signicant dierence in terms of FHR,
reactivity, non-reactivity, variability, deceleration and FHR category distribution (p>0.05). The number of fetal movements was
signicantly (p<0.05) lower in the mask-wearing group.
Conclusion. Mask use should be considered in NSTs where variability is reduced or fetal movements are low. Thus, misinterpre-
tation of the NST can be avoided.
Keywords. COVID-19, face mask, fetal heart rate, non-stress test
ORIGINAL PAPER
Wydawnictwo UR 2023
ISSN 2544-1361 (online)
doi: 10.15584/ejcem.2023.1.14
Corresponding author: Ali Gursoy, e-mail: aligursoy44@hotmail.com
Received: 5.11.2022 / Revised: 18.11.2022 / Accepted: 21.11.2022 / Published: 25.03.2023
Gursoy A, Tekbas ED. Impact of face mask use during the non-stress test in pregnancy. Eur J Clin Exp Med. 2023;21(1):114–119. doi:
10.15584/ejcem.2023.1.14.
ORCID:
OA: https://orcid.org/0000-0002-9999-1865
GA: https://orcid.org/0000-0001-7901-1498
Introduction
Antepartum fetal surveillance aims to reduce mortali-
ty and morbidity during pregnancy. ere are several
methods used for this purpose. ese are maternal per-
ception of fetal movements, non-stress test (NST), con-
traction stress test, umbilical artery doppler velocimetry,
biophysical prole and modied biophysical prole.1
NST is routinely recommended to assess fetal
well-being during the third trimester.2 It is a non-in-
vasive assessment method. Fetal heart rate (FHR), fe-
tal movements, presence of uterine contraction and
deceleration, number of accelerations and reactivity/
non-reactivity are evaluated. If a possible risk is detect-
ed during the evaluation, the decision to perform other
fetal well-being tests or urgent intervention can be dis-
cussed.
COVID-19 was identied in December 2019 in Chi-
na and was declared a pandemic by the World Health
Organization (WHO) on March 2020.3 Although it gen-
erally progresses with clinical ndings such as cough,
fever, loss of taste, loss of smell, shortness of breath,
headache and sore throat, it can also cause serious com-
plications. According to data obtained to date, being in-
fected with COVID-19 during pregnancy may increase
the likelihood of hospitalization, admission to the inten-
sive care unit and need for life support.
Main transmission routes of COVID-19 include
droplet, contact transmission and airborne transmis-

115
Impact of face mask use during the non-stress test in pregnancy
sion. e usage of a disposable medical or surgical
mask that covers the mouth and nose is routinely rec-
ommended to prevent viral transmission. Wearing a
mask, which is the most well-known method of protec-
tion from COVID-19 during the pandemic, continues
in hospital visits as well as daily routine. In a study, it
was determined that the usage of surgical masks in term
pregnancies signicantly reduced oxygen saturation.4
Aim
Based on this nding, we planned to investigate wheth-
er wearing a mask during NST for assessment of fetal
well-being would aect NST results.
Material and methods
Ethical approval
Ethical approval was obtained from Maltepe University
Ethics Committee (No: 2021/900/83) and the study was
carried out in accordance with the principles of the Dec-
laration of Helsinki.
Study design
e study was carried out in Maltepe University Hos-
pital, outpatient clinic of obstetrics between April 2019
and May 2021. A total of 951 pregnant women who
met the criteria were included in the study. Masks have
been routinely used since April 2020 to protect against
COVID infection. Based on this date, two groups as
wearing masks (group B) and not wearing masks (group
A) were created.
ose with a singleton pregnancy and >34 gesta-
tional weeks were included in the study. Exclusion cri-
teria were multiple pregnancy, <34 weeks of gestation,
active labor, maternal disease (hypertension, diabe-
tes mellitus, kidney disease, heart disease) and obstet-
ric risk (preeclampsia, intrauterine growth retardation,
chromosomal or structural abnormality).
e age, body mass index and gestational week were
checked from patient les. FHR, number of acceler-
ations, presence of deceleration and fetal movements
detected in NST were retrospectively analyzed and re-
corded from the archive. All NST recordings were made
by a single device. ose whose NST records could not
be fully analyzed, those with a duration of less than 20
minutes and those with missing data in their les were
not included in the study.
NST interpretation
By following the fetal heart rate tracing in NST; basal
FHR, variability, accelerations, and decelerations can be
measured. FHR is the average beats per minute (bpm)
over a 10-minute interval. e normal value is between
110-160 bpm. Basal FHR <110 bpm is called bradycar-
dia and >160 bpm is called tachycardia. Signicant and
sudden increases in FHR are called accelerations. It is
dened as an increase of ≥15 bpm lasting at least 15 sec-
onds and maximum 2 minutes at ≥32 weeks of gesta-
tion. Absence of accelerations may be associated with
fetal metabolic acidemia and hypoxic injury.5-7
Early decelerations are dened as FHR decreases
with normal variability accompanying uterine contrac-
tions. ey are not associated with hypoxia and acidosis.
Prolonged decelerations are decreases in FHR of at least
15 beats lasting the shortest 2 minutes and the longest
10 minutes. e absence of variability or the presence
of minimal variability and absence of accelerations re-
quires urgent evaluation for hypoxic risk. Variable de-
celerations are sudden drops in FHR. e shape and size
of the deceleration are not related to uterine contrac-
tions. ey account for most decelerations during labor
and reect the baroreceptor-mediated fetal autonom-
ic response to transient mechanical compression of the
umbilical cord. Late decelerations are symmetrical de-
creases and outputs in heart rate together with uterine
contractions. ese decelerations reect the chemore-
ceptor-mediated response to fetal hypoxemia.8,9
Variability occurs depending on the integration of
the sympathetic and parasympathetic systems. A nor-
mal (moderate) variability is dened as the amplitude in
the range of 5-25 bpm. It shows that oxygenation of the
central nervous system is normal, hypoxic damage and
metabolic acidemia are absent.10 Amplitude >25 bpm is
called saltatory pattern and <5 is called minimal vari-
ability.
One of the most important indicator in the eval-
uation of fetal well-being is the reactivity of NST. Re-
active (negative) NST is a normal result showing that
there are accelerations that occur at least 2 times within
a maximum of 20 minutes. Nonreactive (positive) NST
is the absence of two or more accelerations of at least
15 beats lasting, at least 15 seconds within 20 minutes.
While 50% of NSTs are non-reactive under 28 weeks
of gestation, 15% of NSTs between 28-32 weeks are
non-reactive. 1 NST of a normal preterm fetus is usually
non-reactive rather than reactive.
FHR patterns were classied in 3 categories in the
workshop held by the National Institute of Child Health
and Human Development, the American College of Ob-
stetricians and Gynecologists and the Society for Mater-
nal-Fetal Medicine in 2008 (Table 1).6 Category I FHR
monitors predict normal fetal acid-base status at the
time of observation. ey are routinely followed and no
special action is required.7 Category III monitoring is
associated with abnormal fetal acid-base status. In these
cases, a prompt clinical evaluation should be made. To
quickly resolve the abnormal FHR pattern, maternal
oxygen support, change in maternal position, cessation
of labor stimulation, treatment of maternal hypoten-
sion, and treatment of tachysystole can be planned. If
a positive response is not achieved despite the precau-

116 European Journal of Clinical and Experimental Medicine 2023; 21 (1): 114–119
tions taken, delivery can be planned. Category II FHR
follow-ups are uncertain and do not predict abnormal
fetal acid-base status.
Table 1. Three-tier fetal heart rate interpretation system6
CATEGORY I
Category I fetal heart rate (FHR) tracings include all of the following:
•Baseline rate: 110–160 beats per minute (bpm)
•Baseline FHR variability: moderate
•Late or variable decelerations: absent
•Early decelerations: present or absent
•Accelerations: present or absent
CATEGORY II
Category II FHR tracings include all FHR tracings not categorized as Categor y I or Category III.
Category II tracings may represent an appreciable fraction of those encountered in clinical care.
Examples of Category II FHR tracings include any of the following:
Baseline rate
•Bradycardia not accompanied by absent baseline variability
•Tachycardia
Baseline FHR variability
•Minimal baseline variability
•Absent baseline variability not accompanied by recurrent decelerations
•Marked baseline variability
Accelerations
•Absence of induced accelerations after fetal stimulation
Periodic or episodic decelerations
•Recurrent variable decelerations accompanied by minimal or moderate baseline
variability
•Prolonged deceleration ≥2 minutes but <10 minutes
•Recurrent late decelerations with moderate baseline variability
•Variable decelerations with other characteristics, such as slow return to baseline,
“overshoots,” or “shoulders”
CATEGORY III
Category III FHR tracings include either:
•Absent baseline FHR variability and any of the following:
- Recurrent late decelerations
- Recurrent variable decelerations
- Bradycardia
•Sinusoidal pattern
Statistical analysis
In the descriptive statistics of the data mean, standard
deviation, median minimum, maximum, frequency
and ratio values were used. e distribution of vari-
ables was measured with the Kolmogorov Smirnov test.
Mann-Whitney U test was used in the analysis of quan-
titative independent data. Chi-Square test was used in
the analysis of qualitative independent data and the
Fischer test was used when the Chi-Square test condi-
tions were not met. SPSS 28.0 program (IBM, Armonk,
New York, United States) was used in the analysis.
Results
In our study, pregnant women were divided into two
groups because it was planned to examine the eects
of mask use on maternal and fetal oxygenation. Preg-
nant women whose NST data were analyzed in the
pre-pandemic period were named group A and preg-
nant women whose NST data were analyzed during the
pandemic were named group B. In addition, because the
rate of non-reactive NST was found to be higher in the
preterm period than in the term period, the pregnant
women were divided also into subgroups according to
their weeks.
ose between 34-37 gestational weeks were classi-
ed as A1 and B1 groups and those with >37 gestation-
al weeks were classied as A2 and B2 groups. e mean
age of the pregnant women was 31.2±4.9 and their ges-
tational week was between 34+0 and 40+6 (Table 2).
Table 2. Demographic characteristics of all participants
  Min-Max Median Mean±SD/n-%
Age 19 – 44 31 31.2 ± 4.9
Gestational Week 34 – 40.6 37.1 36.8 ± 1.6
FHR 100 – 170 130 129.6 ± 10.1
Non-reactivity     162  17%
Reactivity 789 83%
Variability
I     64  6.7%
II 719 75.6%
III     168  17.7%
FHR Category
I     766  80.5%
II 154 16.2%
III 31 3.3%
Deceleration No     905  95.2%
Yes 46 4.8%
Fetal Movements  0 – 36 9 11.5 ± 8.6
ere was no signicant dierence between the
A1 and B1 groups, in which only pregnancies below
37 weeks were compared in terms of gestational weeks,
FHR, reactivity, non-reactivity, deceleration, FHR cate-
gory distribution and fetal movement number (p>0.05)
(Table 3). e variability in the A1 group was signi-
cantly higher than in the B1 group (p<0.05).
Table 3. Comparison of NST features <37 gestational week
  A1 B1 p
  Mean±SD/n-% Median Mean±SD/n-% Median
Gestational Week 35.5 ± 1.0 35.5 35.5 ± 0.8 35.6 0.858 m
FHR 129.5 ± 10.2 130 130 ± 10.9 130 0.535 m
Non-reactivity 41 17.7% 41 17.1% 0.852 X²
Reactivity 190 82.3% 199 82.9%
Variability
I8 3.5% 15 6.3%
0.027 X²
II 175 75.8% 195 81.3%
III 48 20.8% 30 12.5%
FHR Category
I179 77.5% 197 82.1%
0.482 X²
II 43 18.6% 35 14.6%
III 9 3.9% 8 3.3%
Deceleration No 219 94.8% 227 94.6% 0.914 X²
Yes 12 5.2% 13 5.4%
Fetal Movements 11.4 ± 7.4 9 10.9 ± 8.2 9 0.351 m
m Mann-Whitney U test/X² Ki-kare test
Furthermore, those with pregnancies >37 weeks of
gestation were also analyzed as A2 and B2 groups. ere

117
Impact of face mask use during the non-stress test in pregnancy
was no signicant dierence (p>0.05) in terms of gesta-
tional weeks, FHR, reactivity, non-reactivity, variability,
deceleration and FHR category distribution. Solely, the
number of fetal movements in the B2 group was signi-
cantly (p<0.05) lower than the A2 group (Table 4).
Table 4. Comparison of NST features >37 gestational week
  A2 B2 p
  Mean±SD/n-% Median Mean±SD/n-% Median
Gestational Week 38.2 ± 1 38.1 38 ± 0.8 38 0.259 m
FHR 128.6 ± 9.1 130 130.1 ± 10.2 130 0.134 m
Non-reactivity 34 15.4% 46 17.8% 0.475 X²
Reactivity 187 84.6% 213 82.2%
Variability
I 21 9.5% 20 7.8%
0.609 X²
II 162 73.3% 187 72.5%
III 38 17.2% 52 20.2%
FHR Category
I 185 83.7% 205 79.1%
0.279 X²
II 32 14.5% 44 17.0%
III 4 1.8% 10 3.9%
Deceleration No 215 97.3% 244 94.6% 0.1 X²
Yes 6 2.7% 15 5.8%
Fetal Movements 13 ± 9.1 10 11 ± 9.1 8 0.011 m
Discussion
During pregnancy, maternal and fetal metabolic activi-
ties increase. To compensate these increases, signicant
changes are observed in the respiratory system and car-
diovascular system. Adaptive changes are observed in
static lung volumes, gas exchange and ventilation. Be-
sides, cardiovascular changes such as increased plasma
volume and cardiac output and decreased vascular resis-
tance are also observed.11 In addition to these possible
changes observed during pregnancy, we planned our re-
search considering that the use of masks can also change
respiratory physiology. In our study, we examined the
possible eect of the mask use on NST results. As a pri-
mary outcome, we evaluated the dierence in terms of
FHR, reactivity, non-reactivity, variability, deceleration
rate, FHR category distribution and fetal movements.
e rst usage of mask in the literature was de-
scribed by Mikulicz in 1897. He suggested the usage of
a mouth bandage made of gauze in operations and took
the rst step regarding surgical masks.12 e possible
physiological eects of mask use over time were investi-
gated. While some studies did not show a possible harm
of using masks, some studies showed a disruptive eect
on vital signs. A study by Zhang et al showed that wear-
ing a surgical mask in healthy young people had adverse
eects on cardiopulmonary function during exercise.13
In a similar study, Shaw K et al. showed that wearing a
face mask during exercise had no signicant eect on
healthy young people in terms of percutaneous oxygen
saturation (SpO2), exercise maximum load, tissue oxy-
genation index, exercise hearth rate and rating of per-
ceived exertion.14
On the other hand, it was found that as long as the
surgeons used a mask, their saturation was lower even
if they were within the normal range.15 In a study con-
ducted with 50 university students, it was determined
that the usage of masks caused an increase in heart rate
and a decrease in blood oxygen saturation.16 Lässing et
al. showed that the heart rate and cardiac output were
higher while wearing a surgical mask but there was no
change in the values of blood pressure and blood lactate
level during the exercise.17
Since pregnancy has dierent dynamics, maternal
and fetal eects of mask use during pregnancy have been
investigated for a long time. e physiological changes
detected were variable similar to the general population.
In a study conducted with pregnant healthcare workers
using N95 masks, it was shown that the exhaled oxygen
concentration increased by 3.2% and the exhaled car-
bon dioxide increased by 8.9%. ese values are indica-
tive of increased forced expired CO2 concentration and
decreased forced expired O2 concentration. In contrast,
there was no change in maternal and fetal heart rates,
ngertip capillary lactate levels and oxygen saturation,
and the degree of perceived exertion.18 In a case-con-
trolled study of 48 patients using masks there were no
dierences between the pregnant and non-pregnant in
heart rate, respiratory rate, transcutaneous carbon di-
oxide level and oxygen saturation. Likewise, there was
no signicant eect on FHR.19 A systematic review ex-
amined the physiological eects of N95 face mask use
by pregnant women. It was determined that short-term
usage of N95 ltered face mask did not have a negative
eect on maternal heart rate, respiratory rate, blood ox-
ygen saturation and FHR.20 On the other hand, Roberge
et al. found an increase in subcutaneous CO2 levels over
time during exercise in pregnant women using N95 FFR
face masks.21 In another study supporting this result, it
was determined that the usage of surgical masks in term
pregnancies signicantly reduced oxygen saturation.4
In our study, while examining the pregnant popu-
lation, we paid attention to the distinction of preterm
fetus, which may constitute a handicap. We know that
NST of most preterm fetuses is oen non-reactive.22 In
order to avoid possible misinterpretation that may arise
from this, we compared 34-37 weeks of pregnancy and
>37 weeks of pregnancy as two groups. No negative ef-
fects of mask use on FHR, reactivity rate, non-reactivi-
ty rate, deceleration rate and FHR category distribution
were found in the comparison of both groups (p>0.05).
As negative eects of mask usage, we found a ten-
dency to decrease in variability in the preterm period
and a decrease in the number of fetal movements in the
term period (p <0.05). Fetal movements are one of the
oldest method used to demonstrate fetal well-being. Al-
though fetal movement count is still being used, studies
have not found a proven eectiveness of fetal move-

118 European Journal of Clinical and Experimental Medicine 2023; 21 (1): 114–119
ment count in predicting fetal well-being.23 Location of
the placenta, amniotic uid volume, fetal presentation,
maternal smoking, fetal sex, primiparity, obesity, and
acute exercise have been associated with decreased fetal
movements.24 Similarly, there are many factors that can
aect variability. Possible variables include gestational
week, maternal daily exercise amount, daily rhythm, fe-
tal respiratory movements, fetal gross movements, fetal
behavioral conditions, smoking, fetal gender and ethnic
dierences.25 Since we did not investigate these parame-
ters, we think that the decrease in fetal movement num-
bers or dierences in variability cannot be associated
with the usage of masks alone.
It has been reported that the usage of masks during
physical activities in people with known lung disease
will cause physiological changes, even if minimal. From
this point of view, it can be concluded that attention
should be paid to possible decrease in saturation in pro-
longed NST scans in pregnant women with known lung
disease.26
e negative side eects caused by masks become
more evident over time. Since it can aect many param-
eters such as temperature increase, humidity, facial irri-
tation, itching, headache, acne, vocal fatigue, perceived
voice problems, increased stress, impaired motor func-
tion and cognition, a decrease in the use of masks is ob-
served in the society from time to time.20,27,28 We think
that the most important limitation of our study is that
pregnant women may have removed the mask even for a
short time due to these possible side eects during NST.
Other weaknesses of our study are that we did not ques-
tion the type of masks patients used and how long they
had been wearing them. We state this as another limita-
tion, since CO2 uptake in the dead space increases due to
long-term use of masks and each mask has a dierent l-
ter mechanism.
Conclusion
It seems that the usage of masks will take place in our
lives for a while due to the COVID-19 pandemic. No
signicant eect of mask usage on FHR, reactivity,
non-reactivity, deceleration rate and FHR category dis-
tribution was observed. On the contrary, we determined
that the usage of masks may cause a decrease in baby
movements and a decrease in variability. We think that
possible misinterpretations will be avoided when NSTs
with decreased baby movements and decreased variabil-
ity are evaluated in the light of this information. Pro-
spective studies with large samples are needed for more
comprehensive results on this subject.
Declarations
Funding
is research received no external funding.
Author contributions
Conceptualization, A.G.; Methodology, A.G. and E.D.T.;
Software, A.G..; Validation, A.G. and E.D.T.; For-
mal Analysis, A.G. and E.D.T.; Investigation, A.G. and
E.D.T.; Resources, A.G. and E.D.T.; Data Curation, A.G.
and E.D.T.; Writing – Original Dra Preparation, A.G.
and E.D.T.; Writing – Review & Editing, A.G.; Visual-
ization, A.G.; Supervision, A.G.; Project Administration,
A.G.; Funding Acquisition, A.G.
Conicts of interest
e authors have no conict of interest.
Data availability
e datasets used and/or analyzed during the current
study are open from the corresponding author on rea-
sonable request.
Ethics approval
The study was approved by the Maltepe Universi-
ty Medical Ethics Committee Reference Number No:
2021/900/83.
References
1. American College of Obstetricians and Gynecologists’
Committee on Practice Bulletins—Obstetrics. Antepar-
tum Fetal Surveillance: ACOG Practice Bulletin, Number
229.Obstet Gynecol. 2021;137(6):e116-e127. doi: 10.1097/
AOG.0000000000004410.
2. Hoh JK, Park MI, Park YS, Koh SK. e signicance
of amplitude and duration of fetal heart rate accelera-
tion in non-stress test analysis.Taiwan J Obstet Gynecol.
2012;51(3):397-401. doi: 10.1016/j.tjog.2012.07.014.
3. World Health Organization. WHO Director-General’s
opening remarks at the media brieng on COVID-19 -
11. 2020. Available at: https://www.who.int/dg/speeches/
detail/who-director-general-s-opening-remarks-at-the-
media-brieng-on-covid-19—11-march-2020. Accessed
April 5, 2020.
4. Toprak E, Bulut AN. e eect of mask use on mater-
nal oxygen saturation in term pregnancies during the
COVID-19 process.J Perinat Med. 2020;49(2):148-152.
doi: 10.1515/jpm-2020-0422.
5. Electronic fetal heart rate monitoring: research guidelines
for interpretation. National Institute of Child Health and
Human Development Research Planning Workshop.Am J
Obstet Gynecol. 1997;177(6):1385-1390.
6. Macones GA, Hankins GD, Spong CY, Hauth J, Moore T.
e 2008 National Institute of Child Health and Human
Development workshop report on electronic fetal moni-
toring: update on denitions, interpretation, and research
guidelines. Obstet Gynecol. 2008;112(3):661-666. doi:
10.1097/AOG.0b013e3181841395.
7. ACOG Practice Bulletin No. 106: Intrapartum fetal heart
rate monitoring: nomenclature, interpretation, and general

119
Impact of face mask use during the non-stress test in pregnancy
management principles.Obstet Gynecol. 2009;114(1):192-
202. doi: 10.1097/AOG.0b013e3181aef106.
8. Ayres-de-Campos D, Spong CY, Chandraharan E; FIGO
Intrapartum Fetal Monitoring Expert Consensus Pan-
el. FIGO consensus guidelines on intrapartum fetal
monitoring: Cardiotocography. Int J Gynaecol Obstet.
2015;131(1):13-24. doi: 10.1016/j.ijgo.2015.06.020.
9. Ball RH, Parer JT. e physiologic mechanisms of variable
decelerations.Am J Obstet Gynecol. 1992;166(6 Pt 1):1683-
1689. doi: 10.1016/0002-9378(92)91557-q.
10. Uptodate. Intrapartum fetal heart rate monitoring: Ove-
rview. Available at: http://https://www.uptodate.com/con-
tents/intrapartum-fetal-heart-rate-monitoring-overview
Accessed March 30, 2022.
11. Hegewald MJ, Crapo RO. Respiratory physiology in preg-
na nc y. Clin Chest Med. 2011;32(1):1-13. doi: 10.1016/j.
ccm.2010.11.001.
12. Mikulicz J. Das Operieren in sterilisierten Zwirn-hand-
schuhen undmit Mundbinde. Centralblatt für Chirurgie.
1897;26:714-717.
13. Zhang G, Li M, Zheng M, et al. Eect of Surgical Masks
on Cardiopulmonary Function in Healthy Young Subjects:
A Crossover Study. Front Physiol. 2021;12:710573. doi:
10.3389/fphys.2021.710573.
14. Shaw K, Butcher S, Ko J, Zello GA, Chilibeck PD. Wearing
of Cloth or Disposable Surgical Face Masks has no Eect
on Vigorous Exercise Performance in Healthy Individu-
als.Int J Environ Res Public Health. 2020;17(21):8110. doi:
10.3390/ijerph17218110.
15. Beder A, Büyükkoçak U, Sabuncuoğlu H, Keskil ZA, Ke-
skil S. Preliminary report on surgical mask induced de-
oxygenation during major surgery.Neurocirugia (Astur).
2008;19(2):121-126. doi: 10.1016/s1130-1473(08)70235-5.
16. Tornero-Aguilera JF, Clemente-Suárez VJ. Cognitive and
psychophysiological impact of surgical mask use during
university lessons. Physiol Behav. 2021;234:113342. doi:
10.1016/j.physbeh.2021.113342.
17. Lässing J, Falz R, Pökel C, et al. Eects of surgical face
masks on cardiopulmonary parameters during steady state
exercise. Sci Rep. 2020;10(1):22363. doi: 10.1038/s41598-
020-78643-1.
18. Tong PS, Kale AS, Ng K, et al. Respiratory consequences
of N95-type Mask usage in pregnant healthcare workers-a
controlled clinical study [published correction appears in
Antimicrob Resist Infect Control. 2016;5:26.Antimicrob
Resist Infect Control. 2015;4:48. doi: 10.1186/s13756-015-
0086-z.
19. Roberge RJ, Kim JH, Powell JB. N95 respirator use
during advanced pregnancy. Am J Infect Control.
2014;42(10):1097-1100. doi: 10.1016/j.ajic.2014.06.025.
20. Roeckner JT, Krstić N, Sipe BH, Običan SG. N95 Filtering
Facepiece Respirator Use during Pregnancy: A System-
atic Review.Am J Perinatol. 2020;37(10):995-1001. doi:
10.1055/s-0040-1712475.
21. Roberge RJ, Kim JH, Palmiero A, Powell JB. Eect of Preg-
nancy Upon Facial Anthropometrics and Respirator Fit
Testing. J Occup Environ Hyg. 2015;12(11):761-766. doi:
10.1080/15459624.2015.1049269.
22. Umana OD, Siccardi MA. Prenatal Non-stress Test. [Up-
dated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Is-
land (FL): StatPearls Publishing; 2022 Jan-.Available from:
https://www.ncbi.nlm.nih.gov/books/NBK537123/
23. Kinas MG, Sezer SD, Yuksel H, Odabasi AR. e Role Of
Fetal Movement Amount On Predıctıng e Non-Stress
Test Results. Turk J Obstet Gynecol. 2011;8(4):238. doi:
10.5505/tjod.2011.45822.
24. Sheikh M, Hantoushzadeh S, Shariat M. Maternal percep-
tion of decreased fetal movements from maternal and fetal
perspectives, a cohort study. BMC Pregnancy Childbirth.
2014;14:286. doi: 10.1186/1471-2393-14-286.
25. Zizzo AR, Kirkegaard I, Hansen J, Uldbjerg N, Mølgaard
H. Fetal Heart Rate Variability Is Aected by Fetal Move-
ments: A Systematic Review. Front Physiol. 2020;11:578898.
doi:10.3389/fphys.2020.578898.
26. Epstein D, Korytny A, Isenberg Y, et al. Return to training
in the COVID-19 era: e physiological eects of face ma-
sks during exercise.Scand J Med Sci Sports. 2021;31(1):70-
75. doi: 10.1111/sms.13832.
27. Shekaraiah S, Suresh K. Eect of Face Mask on Voice Pro-
duction During COVID-19 Pandemic: A Systematic Re-
view. J Voice. 2021;S0892-1997(21)00327-1. doi: 10.1016/j.
jvoice.2021.09.027.
28. Rosner E. Adverse Eects of Prolonged Mask Use among
Healthcare Professionals during COVID-19. J Infect Dis
Epidemiol. 2020:6:130. doi: 10.23937/2474-3658/1510130.