FETAL HEART RATE MONITORING


See also Interventions for severe fetal bradycardia

Note--Evidence of benefit to routine electronic fetal monitoring (EFM) in labor is limited. In a randomized trial of 3700 low-risk women in spontaneous labor randomized to admission EFM x 20min vs. Doppler auscultation of FHR, there was no diff. in incidence of neonatal metabolic acidosis, Apgar scores, neonatal resuscitation, or NICU admission. EFM pts sig. more likely to have EFM during labor (OR 1.49), augmentation of labor (OR 1.33), or operative delivery (OR 1.36) (BMJ 322:1457, 2001--JW)

I. Can be done intrapartum or for antepartum assessment of fetal well-being ("NST")

  1. 65% of 28-wk fetuses will have a reactive NST
  2. 85% of 32-wk fetuses will have a reactive NST
  3. 95% of 34-wk fetuses will have a reactive NST

II. Biweekly NST's in fetuses who need monitoring may bring better outcomes than weekly NST's (Obs. Gyn 67:566, 1986, cited in AFP 56:1981, 1997)

III. Normal parameters

  1. Normal FHR at term is 110 (or 120 according to some) - 160
  2. Short term variability (aka "beat-to-beat") avg = 2-3 BPM
  3. > 25 = "saltatory"--not grave; us. from ephedrine
  4. Long term variability (over 10-20 sec) nl = 5-15 BPM
  5. LTV without STV is rare, can be "sinusoidal" which us. represents fetal anemia--very grave
  6. Fetuses can have sleep cycles lasting up to 40min, so may have to monitor for 1h for an NST

IV. Physiologic influences on fetal heart rate:

  1. Baroreceptors in aortic arch & carotid bodies
  2. Chemoreceptors respond to decrease in PO2 & increases in PCO2 with
  3. Variability is a CNS phenomenon, & can be diminished in asphyxia, exogenous narcosis, & sleep

V. Decelerations:

  1. Variable: variable in contour & timing; us. fast down & fast back up; result from temporary occlusion of umbilical artery, resulting fetal hypertension, and thus vagal-mediated fetal bradycardia.Mild & mod. are common (50-80% of labors) and benign. Repetitive severe variables can be treated with position changes, O2, and amnioinfusion
    1. "Mild"--remain above 80 BPM and last < 30sec
    2. "Moderate"--70-80BPM and last 30-60sec
    3. "Severe" < 70BPM and last > 60sec--can represent significant asphyxia
    4. Benign indicators: rapid descent and recovery, good baseline variability between decels, acceleration "shoulders" at onset & and
    5. Ominous indicators: late onset w/respect to ctx, slow recovery, decreased variability between decels, fetal tachycardia, loss of "shoulders"
  2. Late
  1. Slow onset & recovery, nadir generally after peak of contraction
  2. Mediated by hypoxemia sensed by chemoreceptors
  3. A few lates are normal; persistent ones are ominous
  4. Magnitude of lates does not have any predictive value
  1. Early: An old term; may not represent a distinct entity; may actually represent lates
  2. Causes of sudden fetal bradycardia
    1. Uterine rupture, esp. in a VBC--CAN BE THE ONLY SIGN OF UTERINE RUPTURE! IUPC readings can still be NORMAL, and pain can be absent!
    2. Cord prolapse
    3. Fetal hemorrhage
    4. Abruptio placentae

VI. See also Intervention for severe fetal bradycardia

VII. Intermittent auscultation of fetal heart rate as an alternative to continuous electronic fetal monitoring:

  1. Low risk patient: Start in active phase of stage 1; do Q15-30min; in stage 2, do Q5min or after each contraction
  2. Each time: Count FHR x 1min between ctx and 1min after ctx

VIII. Other adjunctive assessment techniques for FHR monitoring

  1. Acoustic stimulation
  2. Scalp stimulation
  3. Fetal scalp blood pH

IX. Mnemonic for assessing fetal well-being intrapartum: "DR C BRAVADO"

Determine Risk--Assess prenatal and intrapartum risk factors and labor progress

Contractions (determine by palpation, tocometer, or IUPC)--Adequate?  Hypertonic?

Baseline Fetal Heart Rate--Should be 110-160 BPM, requires 10min monitoring to establish; bradycardia = < 110; severe bradycardia = < 100; tachycardia = > 160, severe tachycardia = > 200 (note; the latter can be from fetal congenital heart disease)

Variability--Normal = 10-15BPM around baseline; more accurately assessed w/FSE; best predictor of good fetal outcome (better than accels); decreased with sleep, hypoxia, acidosis, prematurity, CNS anomalies, and drugs including narcotics

Accelerations--Requires > 15BPM over baseline x > 15sec; presence is reassuring

Decelerations--Must correlate with timing of contractions to classify

Overall assessment