Obgyno Wino Podcast Episode 88 - Intrapartum Fetal Heart Rate Monitoring and Management
“As the Hindu sages who fashioned the Akashic concept realized, there are aspects of the human mind that are unlimited in space, therefore omnipresent, and that are also boundless in time, therefore eternal and immortal." - Ervin Laszlo
PB#106 - Published July 2009 (Reaffirmed 2017) PB#116 - Published November 2010 (Reaffirmed 2017)
1. The widespread use of continuous electronic fetal monitoring has not been shown to significantly affect such outcomes as perinatal death and cerebral palsy when used for women with low-risk pregnancies.
2. Cat 2 tracings should prompt more frequent reassessment and conservative interventions to improve it.
3. Cat 3 tracings should prompt immediate intervention and expedited delivery is improvement is not achieved.
4. Many medications can cause changes to the FHR tracing, but none of these changes have been found to be associated with worse fetal outcomes, though they often lead to interventions like c-section
5. No accelerations? try acoustic stimulation just above the pubic symphysis OR massaging the fetal scalp with your finger
Why do we care to monitor fetal heart rate intrapartum?
- antepartum complications can lead to fetal/neonatal morbidity and mortality, so we use a continuous fetal heart tracing to try to predict fetal acidemia
- even fetuses without risk factors are can become hypoxic (one study of 63% of term pregnancies affected by fetal hypoxia had no risk factors)
- unfortunately, there are significant limitations to to this technology AND even trained clinicians often disagree with their interpretation of tracings
- in one study four OBGYNS were asked to reviewed 50 intrapartum FHR tracings; they agreed in their interpretation of only 22%; 2 months later, the same four OBGYNs were asked to reinterpret the same 50 tracings, and they interpreted 21% of these same tracings in a different way (facepalm!)
- OBGYNs are more consistent in their interpretation when the fetal outcome is known (which is why this is a useless reference for
- as a result, the literature doesn't exactly support the widespread use of continuous EFM (though nobody seems to have a better idea for intrapartum fetal monitoring)
Exhibit A: "Of infants who are born with metabolic acidemia, only approximately one-half potentially could be identified and have delivery expedited even under ideal circumstances, which are probably not realistic in current US practice." (Retrospective study in the Grey Journal)
Exhibit B: "Despite 80 years of studies in clinical cohorts and animal models, the field of research on intrapartum fEEG is still nascent and shows great promise to augment the currently practiced electronic fetal monitoring." (Systematic Review)
Exhibit C: "After more than half a century, interpretation of fetal heart rate tracings remains as much an art as it is a science." (Systematic Review in the Green Journal)
**There are also a few OBGYNs who have made a post-retirement career out of testifying against their colleagues based on their own, very selective practice of tracing interpretation. See Exhibit E.
Continuous FHR monitoring isn't necessary in low-risk birth
- the limitations of continuous FHR monitoring lead to high rates of intervention (high false positive rates), especially in low-risk birth
- despite these limitations, nearly every hospital-based birth is monitored continuously unless asked for specifically by the patient
- we can buck this trend for low-risk births by acknowledging what ACOG published in Committee Opinion No. 766: Approaches to Limit Intervention During Labor and Birth:
"The widespread use of continuous electronic fetal monitoring has not been shown to significantly affect such outcomes as perinatal death and cerebral palsy when used for women with low-risk pregnancies."
Continuous monitoring can be done in two ways
- externally: Doppler paddle is applied to the abdomen
- internally: a little electrode is screwed into the scalp skin of the fetus
- "normal" contraction pattern: ≤5 contractions in a 10-minute over 30-minutes of observation
- tachysystole: >5 contractions in a 10-minute over 30-minutes of observation
- when you use the word tachysystole, you must ALWAYS further qualify them as to the presence or absence of associated FHR decelerations
- the term "recurrent" can be used to qualify decelerations that are associated with at least 50% of contractions
FHR tracing categorization
- cat 1: all good, low risk for fetal acidemia ->> routine monitoring
- cat 2: unlikely fetal acidemia, though fetal acidemia may develop if intervention doesn't improve the tracing
- cat 3: likely fetal acidemia, therefore if immediate interventions aren't helpful to improve the tracing, expedited delivery may be recommended
What kinds of interventions might improve a FHR tracing?
- maternal repositioning to decompress the maternal vena cava or cord)
- amnioinfusion (esp for recurrent variable decels)
- correction of serum blood sugar
- boosting blood pressure (e.g. epinephrine, ephedrine, or phenylephrine)
- slowing down uterine contractions or temporarily stopping them (e.g. administer β̞₂-agonist)
- improving maternal oxygenation (e.g. open airways, optimize ambient oxygen)
- stop oxytocin
- raise the patient's legs
Note: It may also be helpful to review this FREAKIN FANTASTIC article titled "The physiology of intrapartum fetal compromise at term".
Late decelerations should prompt intervention
- they reflect either transient or chronic uteroplacental insufficiency, but they have a low positive predictive value for neurologic injury in the infant
- if you still see moderate variability (even in absence of accelerations), you probably still have time to work through external resuscitative measures
Fetal tachycardia often reflects chorioamnionitis, but not always...
- other infections should also be considered (e.g. pyelonephritis), but positive predictive value is quite low in absence of fever
- terbutaline, cocaine, and other stimulants can also be responsible
- along with hyperthyroidism, placental abruption, fetal bleeding, or fetal tachyarrhythmias (esp. if >200 bpm)
- make sure you are distinguishing fetal from maternal HR
- if it's, indeed, fetal: is it a prolonged decel? (>2 min but <10 min)
- >10 min is defined as fetal bradycardia
- causes include: maternal hypotension (e.g. post-epidural)
How often should I reassess the FHR tracing while on continuous monitoring?
- q30 minutes in 1st stage
- q15 minutes in 2nd stage
- as frequently as q5 minutes if significant maternal or fetal comorbidities that might predispose the fetus to acidemia
What's the alternative to continuous FHR monitoring?
- intermittent auscultation: pop on the monitors q15 minutes in 1st stage, q5 minutes in 2nd stage
- not recommended for high-risk pregnancies (e.g. fetal growth restriction, preeclampsia, and type 1 diabetes)
- aim to monitor through at least one contraction to evaluate for decelerations
What about pre-term babies?
- this technology has even higher false positive rates pre-term
- remember that the parasympathetic nervous system develops after the sympathetic nervous system, therefore, the push and pull of the fetal nervous system to restitute as a "normal" tracing pattern may not even be established until >32 wga
- for example, variable decelerations are more common at <37 wga (seen 55-70% of the time versus 20-30% of the time at term)
- use your entire clinical picture in decision-making while monitoring preterm fetuses
Medications that can influence FHR tracing
- epidural anesthesia containing local anesthetic (e.g. lidocaine, bupivacaine): sympathetic blockade may cause maternal hypotension resulting in decreased variability or the appearance of decelerations (this effect is more likely with combined spinal-epidural anesthesia)
- meperidine: bradycardia
- narcotics: decreased variability and disappearance of accelerations; less fetal breathing movements
- magnesium sulfate: decreased variability (esp for pre-term fetuses)
- butorphanol: sinusoidal pattern
- cocaine: increased contraction frequency and fetal tachycardia
- nalbuphine: less frequent accelerations
- corticosteroids: decreased variability (transient: will resolve in 4-7 days)
**Note: None of these changes in tracing were associated with worse fetal outcomes, though they often lead to interventions like c-section
At a mere glance of the FHR tracing, how might one determine that fetal acid-base status is OK?
- if you see moderate variability, then everything is dandy (even better if you detect accelerations)
- the presence of moderate variability alone is strongly associated with arterial umbilical pH of >7.15
- even in the presence of moderate or late decelerations, arterial umbilical pH is probably >7.00 if variability is moderate
What can I do to further assess the fetus in the case of a Cat 2 or Cat 3 tracing?
- no accelerations? try acoustic stimulation just above the pubic symphysis OR massaging the fetal scalp with your finger (variability decreases during fetal sleep cycle)
- cat 3 tracing? fetal scalp blood sampling is an option but exceedingly rare nowadays