1. INTRAPARTUM ASSESSMENT
Ch. 14.
INTRAPARTUM ASSESSMENT
부산백병원 산부인과
R1 손영실

2. # Intrapartum Fetal Assessment

3. INDEX 1. Internal Electronic Fetal Hearth Rate Monitoring
2. External (Indirect) Electronic Fetal Heart Rate
3. Fetal Heart Rate Pattern
- Baseline Fetal Heart Activity

4. ◎ Continuous graph paper of fetal heart rate
- Potentially diagnostic in assessing pathophysiological
events affecting the fetus
① Electronic fetal heart rate monitoring provided accurate
information
② The information was of value in diagnosing fetal
distress
③ It would be possible to intervene to prevent fetal death
or morbidity
④ Continuous electronic fetal heart rate monitoring was
superior to intermittent methods

5. FETAL HEART RATE MONITORING
INTERNAL ELECTRONIC
FETAL HEART RATE MONITORING
◎ Measured by attaching a bipolar spiral electrode
directly to the fetus
- the wire electrode penetrate the fetal scalp and the
second pole is the metal wing on the electrode
- vaginal body fluids create a saline electrical bridges
that completes the circuits and permits measurement
of the voltage differences between two poles
◎ The electrical fetal cardiac signal – P wave, QRS
complex, and T wave – is amplified and fed into a
cardiotachometer for heart rate calculation

6. FETAL HEART RATE MONITORING
INTERNAL ELECTRONIC
FETAL HEART RATE MONITORING
◎ Electrical cardiac complexes detected by electrodes
include those generated by mother
- maternal ECG signal is approximately five times stronger
than fetal ECG
- but, its amplitude is diminished when it is recorded
through fetal scalp electrode
① In a live fetus
- this low maternal ECG signal is detected but masked
by the fetal ECG
② If the fetus is dead
- the weaker maternal signal will be amplified by the
automatic gain control circuitry in the fetal monitor
and displayed as “fetal” heart rate

7. FETAL HEART RATE MONITORING
INTERNAL ELECTRONIC
FETAL HEART RATE MONITORING
Standard fetal monitor tracing of heart rate using fetal scalp electrode shown at top. Bottom two tracings represent cardiac electrical complexes detected from fetal scalp and maternal chest wall electrodes. Spiking of the fetal rate in the monitor tracing is due to the premature atrial contractions. (F=fetus; M=mother; PAC=fetal premature atrial contraction.)

8. FETAL HEART RATE MONITORING
INTERNAL ELECTRONIC
FETAL HEART RATE MONITORING
Placental abruption: The fetal scalp electrode detected heart rate first of the dying fetus. After fetal death, the maternal ECG complex is detected and recorded.

9. EXTERNAL (INDIRECT) ELECTRONIC FETAL HEART RATE MONITORING
◎ External detectors to monitor
fetal heart and uterine action
⇒ the necessity for membrane
rupture and uterine invasion
may be avoided
◎ FHR (fetal heart rate)
⇒ detected through the
maternal abdominal wall
using the ultrasound Doppler
principle

10. EXTERNAL (INDIRECT) ELECTRONIC FETAL HEART RATE MONITORING
◎ Consist of the unit
① transducer - emits ultrasound
② sensor - detect a shift in frequency of the reflected
sound
• transducer
⇒ placed on the maternal abdomen at a site where fetal
heart action is best detected
• coupling gel must be applied
(∵ air conducts ultrasound poorly)
• the device is held in position by a belt
• care should be taken that maternal aortic ulsations are not
confused with fetal cardiac motion

11. FETAL HEART RATE PATTERNS
◎ Scaling factors (by the workshop)
- 30 bpm per vertical cm (range, 30 to 240 bpm)
- 3 cm/min chart recorder paper speed
# Baseline fetal heart activity
1) Rate
• with increasing fetal maturation
→ the heart rate decreases
• baseline FHR decreased
an average of 24 bpm (between 16 weeks and term)
approximately 1 bpm/week
• weeks : 160 bpm
40 weeks : 150 bpm

12. FETAL HEART RATE PATTERNS
• during 3rd trimester, normal mean FHR is between 120
and 160 bpm
baseline FHR less than 110 bpm
⇒ bradycardia
baseline FHR greater than 160 bpm
⇒ tachycardia
sympathetic system
⇒ accelerator influence
parasympathetic system
⇒ decelerator factor mediated via vagal slowing
of heart rate

13. FETAL HEART RATE PATTERNS
A. Bradycardia
• mild bradycardia
: 100 ~ 119 bpm
- observed in 2% of monitored pregnancies, averaged
about 50 minutes in duration
- attributed to head compression from occiput posterior
or transverse positions, particularly during 2nd stage
labor
• moderate bradycardia
: 80 ~ 100 bpm
• severe bradycardia
: less than 80 bpm

14. FETAL HEART RATE PATTERNS
• other cause
: congenital heart block and serious fetal
compromise
Fetal bradycardia measured with a scalp electrode in a pregnancy complicated by placental abruption and subsequent fetal death.

15. FETAL HEART RATE PATTERNS
B. Tachycardia
• mild : 161 ~ 180 bpm
severe : 181 bpm or more
• cause
maternal fever from amnionitis (m/c)
fetal compromise
cardiac arrhythmias
parasympathetic (atropine) or sympathomimetic
(terbutaline) drugs
• fetal compromise with tachycardia
⇒ concomitant heart rate deceleration (key point)

16. FETAL HEART RATE PATTERNS
2) Beat-to-beat variability
• an important index of cardiovascular function
• regulated largely by the autonomic nervous system
A. Short-term variability
• instantaneous change in FHR from one beat to the next
• time interval between cardiac systoles

17. FETAL HEART RATE PATTERNS
B. Long-term variability
• the oscillatory changes that occur during the course
of 1 minute
- result in waviness of the baseline
- normal frequency : 3 ~ 5 cycle/min

18. FETAL HEART RATE PATTERNS
• physiological and pathological processes
(affect or interfere with beat-to-beat variability)
① fetal breathing
② fetal body movements
③ advancing gestation
- after 30 wks,
fetal inactivity
→ diminished variability
activity
→ variability increased

19. FETAL HEART RATE PATTERNS
④ maternal acidemia
- cause decreased fetal beat-to-beat variability
⑤ analgesic drugs given during labor
- diminished variability
(narcotics, barbiturates, phenothiazines,
tranquilizer)
- MgSO4
: decrease variability only in the third hour of
the infusion
: be deemed clinically insignificant
: blunted the frequency of acceleration

20. FETAL HEART RATE PATTERNS
Grades of baseline fetal heart rate variability. (1) Undetectable, absent variability; (2) minimal≤5 bpm variability; (3) moderate (normal), 6 to 25 bpm variability; (4) marked,＞25 bpm variability; (5) sinusoidal pattern.

21. FETAL HEART RATE PATTERNS
3) Cardiac arrhythmia
◎ first suspected signs
- baseline bradycardia
- tachycardia
- abrupt baseline spiking (m/c)

22. FETAL HEART RATE PATTERNS
4) Sinusoidal heart rates
◎ true sinusoidal pattern
- observed with serious fetal anemia
• from D-isoimmunization
• ruptured vasa previa
• fetomaternal hemorrhage
• twin to twin transfusion
◎ insignificant sinusoidal pattern
• administration of meperidine, morphine, alphaprodine,
and butorphanol
• amnionitis, fetal distress, and umbilical cord
occlusion

23. FETAL HEART RATE PATTERNS
◎ definition
① stable baseline heart rate of 120 ~ 160 bpm with
regular oscillations
② amplitude of 5 ~ 15 bpm (rarely greater)
③ frequency of 2 ~ 5 cycles/min long-term variability
④ fixed or flat short-term variability
⑤ oscillation of the sinusoidal waveform above or
below a baseline
⑥ absence of accelerations

24. FETAL HEART RATE PATTERNS
◎ pathophysiology of sinusoidal patterns is unclear
Sinusoidal fetal heart rate pattern associated with maternal intravenous meperidine administration. Sine waves are occurring at a rate of 6 cycles/min.

25. 감사합니다.