J. Perinat. Med. 2015; x(x): xxx–xxx

Toshiyuki Uchida, Naohiro Kanayama*, Mari Mukai, Naomi Furuta, Hiroaki Itoh,Hikaru Suzuki and Masatsugu Niwayama

Examiner’s finger-mounted fetal tissue oximetry:a preliminary report on 30 cases
Abstract
Objective: To describe preliminary experience with afinger-mounted fetal tissue oximetry probe during the 2ndstage of labor.
Materials and methods: A total of 30 term pregnant
women without pregnancy complications were recruited.
We measured fetal tissue oxygen saturation (FtO2) byusing a finger-mounted fetal tissue oximetry during cervical examinations in the 2nd stage of labor. The data capturing rate of FtO2 and the interclass correlation coefficientwere also examined. The mean FtO2 was compared to theneonatal condition assessed by the levels of umbilicalcord blood.
Results: FtO2 was obtained in all cases, regardless ofwetness, hair color, the part of the fetal head that wasexposed, rotation of the fetus, color of amniotic fluid, andcaput succedaneum. The mean FtO2 was 65.5%±8.58% in
normal neonates [Apgar score > 7 (1 min), n = 25]. The mean
FtO2 was significantly correlated with umbilical cord arterial pH (r = 0.52, P = 0.0030, n = 30), but not with umbilicalcord arterial partial pressure of oxygen. The interclass correlation coefficient was 0.94.
Conclusions: Tissue oxygen saturation of the fetal head
was obtained easily by the examiner’s finger-mounted
fetal tissue oximetry.
Keywords: Examiner; fetal tissue oximetry; fetal tissue
Q1:
Please check oxygen saturation; finger pulp; near-infrared spectrosand confirm copy; parturition.
the affiliations for corresponding
author andco-authors. **Corresponding author: Naohiro Kanayama, MD, PhD, Departmentof Obstetrics and Gynecology, Hamamatsu University School ofQ2:
Please sup- Medicine, 1-20-1 Handa-yama, Hamamatsu 431-3192, Japan,
ply complete Tel.: +81-453-435-2309, Fax: +81-453-435-2308,
E-mail: kanayama@hama-med.ac.jp
affiliation
comprising Toshiyuki Uchida, Mari Mukai, Naomi Furuta and Hiroaki Itoh:(department, Department of Obstetrics and Gynecology, Hamamatsu University
School of Medicine, Japanuniversity…etc) forHikaru Suzuki: ASTEM Co., Ltd., Kawasaki, Japanauthor
Masatsugu Niwayama: Department of Electrical and Electronics“HikaruEngineering, Shizuoka University, Japan; and Research Institute ofSuzuki”.
Electronics, Shizuoka University, Japan

DOI 10.1515/jpm-2014-0297
Received September 4, 2014. Accepted February 10, 2015.

Introduction
The best approach to evaluate fetal well-being is tomeasure fetal blood pressure and oxygen status, whichcannot be achieved non-invasively using currently available techniques. Therefore, fetal heart rate (FHR) is thegold standard for evaluating fetal status. However, FHR
monitoring has shown to have low false-negative andhigh false-positive rates [1]. Thus, obstetricians haveattempted to use fetal oxygen status, by itself or in addition to FHR monitoring, to improve diagnostic ability[2–4].
There have been many reports describing thedevelopment of fetal pulse oximetry, and subsequentclinical trials investigating the technique [5–7]. Several
researchers have reported that oxygen dynamics can bemeasured using a pulse oximetry probe applied transvaginally to the fetal head [8–10]. In addition, an intravaginal optical probe using near-infrared spectroscopy(NIRS) to measure fetal oximetry has also been reported[11, 12]. However, East et al have reported that every
method has a significant rate of signal loss during theactive phase of labor, and sensor contact is lost during
oximetry in up to 64% of attempts [13]. The markedly
low rate of data capture inherent in these approaches
remains one of the most significant barriers in adopting
these procedures. Other drawbacks include the invasiveness of the probe, patient discomfort, and interferencewith the obstetrician performing cervical examinations. Although many clinical trials investigating fetal
pulse oximetry have been performed, its clinical utility
remains controversial [10].
Recently, we developed a new approach to fetal tissue
oximetry [14], which changes the placement of the sensor
to overcome these issues. We attached an NIRS probe to
the doctor’s finger, rather than the fetal head or cheek.
Here we report the characteristics of this oximetry technique and clinical data obtained during labor.

Q3:
Please confirm runninghead.

2

Uchida et al., Examiner’s finger-mounted fetal tissue oximetry: a preliminary report on 30 cases

Materials and methods
Probe

Q4:
Pleasesupply themanufacturer’s name,city, andcountry for
all reagents,devices, andsoftware
mentioned
throughout.

The wavelengths of the light sources were 770 nm and 810 nm, andthe sensitivity of the photodiodes (PD2501, Epitex) was high in thenear-infrared band. The bare chips of the light-emitting diodes(LEDs) and photodiodes were mounted on the substrate with a wirebonding. The detectors were located 6 mm and 8 mm away from theLEDs to determine the absolute value of hemoglobin concentration
using the spatially resolved NIRS (Figure 1A).

Patients

Results

Pregnant women who were at term and had not experienced any
complications during their pregnancy were recruited for the presentstudy. Informed consent was obtained from the subjects, and the protocol was approved by the Ethics Committee of Hamamatsu University School of Medicine.

Measurement protocol
We measured fetal tissue oxygen saturation (FtO2) in the late 2nd stageof labor until delivery. The probe was attached to the fetus head during

LEDs

the delivery. Each measurement lasted at least 1 min after the attachment of the sensor. For the measurement, transparent vinyl gloves
were prepared in collaboration with Utsunomiya Seisaku Co., Ltd.
(Higashi Osaka-shi, Japan). Figure 1 (B, C, and D) shows the examiner’s
finger with the optical probe the method for data capture. To calculate
the interclass correlation coefficient, the measurement was also performed for three cases, that is, three different obstetricians measured
FtO2 in each patient. The umbilical artery pH and partial pressure ofoxygen (PaO2) were measured at the time of the delivery. Statisticalsignificance was calculated by Spearman’s correlation coefficient. The
value of P < 0.05 was considered to be statistically significant.

Photodiodes

A total of 30 women were recruited in the study. The characteristics of the participants are presented in Table 1.
FtO2 was obtained in all cases, regardless of wetness, haircolor, the part of the fetal head that was exposed, rotation of the fetus, color of amniotic fluid, and caput succedaneum. After attachment of the sensor to the fetalhead, we obtained FtO2 within 10 s in all the cases. The
measurement was performed between one and five times
during each delivery, and FtO2 was obtained at every

BA

5 mmCD

Microcomputer
unit

Figure 1: Scheme (A) and photograph (B) of the oximeter probe attached to the examiner’s finger pulp. Flexible substrate-mounted twolight-emitting diodes (LEDs) and two photodiodes are adhered to a black rubber sheet. (C) The outlook of the measurement. (D) The measurement of the newborn.

3Uchida et al., Examiner’s finger-mounted fetal tissue oximetry: a preliminary report on 30 cases

80

Table 1: The characteristics of the subjects.

7032 (24–42)
0 (0–1)281 (261–293)3143 (2276–3970)
7.305 (7.054–7.382)
8 (5–10)9 (7–10)
4.54 (1–15.3)
114 (3–969)

Values are expressed as median (range).

60
FtO2 (%)

Age (years)
ParityGestational age (days)
Birth weight (g)Umbilical artery pH
Apgar score (1 min)Apgar score (5 min)Measurement time (min)Time of second stage (min)50
40
y=0.251x+59.709
R2 =0.0295(P=0.36, N=30)

30
20
10
00measurement. The rate of continuous data capture was
100% during the initial 1 min, 63.3% during the sequential
3 min, and 46.7% during the entire 5 min. The interclasscorrelation coefficient was 0.94.
The mean FtO2 was 65.5%±8.58% (n = 25) when the 1 min
Apgar score was > 7 (correlation coefficient 0.25; P = 0.19).
The relationship between mean FtO2 and umbilical artery
pH is presented in Figure 2 (n = 30), (correlation coefficient0.52; P = 0.0030). The relationship between mean FtO2 andumbilical artery PaO2 is presented in Figure 3 (n = 30), (correlation coefficient 0.17; P = 0.36). There was only one casein which the umbilical artery pH was < 7.1. The mean FtO2
in this case was 41.7%. Representative plots of cases withnormal FtO2 and low FtO2 are shown in Figure 4A and B.

1020UA-PaO2 (mm Hg)

3040Figure 3: There is no significant correlation between umbilicalartery partial pressure of oxygen (UA-PaO2) and fetal tissue oxygen
saturation (FtO2).

Discussion
We have developed a fetal tissue oximetry techniqueinvolving a probe mounted on the examiner’s finger [14].

8070FtO2 (%)

60
50
40
y=64.978x–408.73
R2=0.2746(P=0.0030, N=30)

30
20
100
7

7.1

7.2

7.3

7.4

UA-pH
Figure 2: There is a significant relationship between umbilical cordarterial pH (UA-pH) and fetal tissue oxygen saturation (FtO2).

Figure 4: (A) Normal FtO2 case. The patient was a 34-year-old primigravida who delivered her infant at the 38th gestational week. Theinfant had the Apgar score of 9 at 1 min and 9 at 5 min, and weighed
2870 g. The umbilical artery pH was 7.27. The mean FtO2 was 64.4%.
(B) Low FtO2 case. The patient was a 31-year-old parous woman who
had a delivery at the 38th gestational week. The infant had the Apgar
score of 8 at 1 min and 8 at 5 min. The umbilical artery pH was 7.05.
The mean FtO2 was 41.7%.

4Uchida et al., Examiner’s finger-mounted fetal tissue oximetry: a preliminary report on 30 cases

During the present study, we succeeded in obtaining FtO2
measurements in all cases. Previous research has revealed
that the presence of dark, thick, curly hair makes sensor
attachment difficult [15] and may be a source of artifact
because it absorbs red light and affects the error/signal
ratio; a signal was also difficult to obtain during theappearance and expression of the fetal head. In our study,
we were able to obtain a signal promptly in all cases; thiswas not impacted by wetness, hair color, the part of the
exposed fetal head, fetal rotation, amniotic fluid color,
caput succedaneum, or fetal head expression. Previous
fetal pulse oximetry (FpO2) devices were found to havedata capture rates of approximately 70% owing to inadequate contact between the sensor and fetal skin. Because
our sensor was constantly attached to the fetal head, weobtained a data capture rate of 100% during the 1st min
and then the signal gradually decreased owing to fatigue
of examiner’s finger.
Continuous O2 monitoring may be beneficial if
it enables prompt diagnosis and treatment of fetal
asphyxia. Rapid measurements of oxygen saturation at
multiple sites are needed to document asphyxia. Commercially available sensors are placed on one locationof the fetal head for the monitoring period, whereas thefinger-based probe that we developed can be moved to
any location accessible to the obstetrician. In addition,
the spatially resolved NIRS system that we used candetect tissue oxygenation in low-perfusion conditions,which may allow a signal to be obtained in more clinical scenarios than previous designs. Our sensor achieves
this because it requires only spatial intensity slope andnot the weak pulsation signals that a traditional pulse
oximetry requires. We assessed the readings obtained bymultiple examiners to determine whether the amount ofpressure applied to the fetal head would influence theFtO2 values. We found an interclass correlation coefficient of 0.94, which suggests that the amount of pressure
has limited to no effect.
Many investigators have reported that FpO2 in a typicalnd
2 stage of labor was approximately 50%. Our FtO2 wasslightly higher (65.5%±8.58%) than that reported withFpO2, suggesting that our value is a mixed measurementof the scalp and the brain. We have previously reported
that our FtO2 reflects contributions of approximately twothirds from the fetal brain and approximately one-thirdfrom the scalp, and we assume that this is the reason
for our FtO2 to be higher than previously published FpO2
data. We believe that our findings are correct as they correlate well with published data on the cerebral tissue
oxygen saturation in neonates (67%–80%) [16, 17]. The
present study is the first to report data on tissue oxygen

saturation of the fetal head during labor. Because theinformation obtained using our technique provides information on both the scalp and the brain, we believe it may
be useful in clinical practice.
Our FtO2 data also correlated well with neonatal
parameters. There was a significant correlation between
FtO2 and umbilical artery pH, whereas no correlation wasobserved between FtO2 and umbilical artery PaO2. Because
our tissue oxygen saturation measures reflect the peripheral oxygen status of the brain and scalp, we believe thatthe FtO2 value should differ from PaO2 value. We had one
neonate with an umbilical artery pH < 7.1, and a mean FtO2of 41.7% was recorded in this case. The woman was parousand without complications during her pregnancy. Thelabor was notable for severe recurrent variable deceleration during the second stage of labor. The FtO2 trend wascontinuously < 50% (Figure 4B). The Kristeller maneuver(fundal pressure) was performed to hasten delivery, and
the Apgar scores were 8 at 1 min and 8 at 5 min. This casehighlights the possible clinical significance of oximetry
measures obtained using our technique.
Our study was limited only by its small size (only 30cases), the exclusion of women with complications, andthe lack of compromised fetuses. Despite these limitations,the present study demonstrates the ease and simplicity of
our finger-based device to obtain quick and reliable FtO2
measurements. We believe that our oximetry probe provides new information for fetal management. We are currently conducting multicenter studies in Japan to better
assess the clinical utility of our approach for determining
fetal oxygen saturation.
Acknowledgments: We would like to thank Mr. Yutaka
Yokoyama and Yukio Chitose of ASTEM Co., Ltd., Kawasaki, Japan for advice in the development of the instruments. We acknowledge the financial support of theAdaptable and Seamless Technology transfer Program
through target driven R&D (A-STEP) program from theJapan Science and Technology Agency (JST).

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The authors stated that there are no conflicts of interest regarding
the publication of this article.