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OB34 Obstetrics
Normal Labour and Delivery Toronto Notes 2019
Intrapartum Fetal Monitoring
• intermittentfetalauscultationwithDopplerdeviceq15-30minfor1mininfirststageactivephase following a contraction, q5min during second stage when pushing has begun
• continuouselectronicFHRmonitoringreservedforabnormalauscultation,prolongedlabour,labour which is induced or augmented, meconium present, multiple gestation/fetal complication
■ use of continuous electronic monitoring shown to lead to higher intervention rates and no improvement in outcome for the neonate when used routinely in all patients (i.e. no risk factors)
■ techniques for continuous monitoring include external (Doppler) vs. internal (fetal scalp electrode) monitoring
• fetalscalpsamplingshouldbeusedinconjunctionwithelectronicFHRmonitoringandcontraction monitoring (CTG) to resolve the interpretation of abnormal or atypical patterns
Electronic FHR Monitoring
• FHRmeasuredbyDoppler;contractionsmeasuredbytocometer
Approach to the Management of Abnormal FHR
POISON – ER
Position (left lateral decubitus position) O2 (100% by mask)
IV fluids (corrects maternal hypotension) Fetal scalp stimulation
Fetal scalp electrode
Fetal scalp pH
Stop oxytocin
Notify MD
Vaginal exam to rule out cord prolapse Rule out fever, dehydration, drug effects, prematurity
• If above fails, consider C/S
Continuous CTG as a Form of EFM for Fetal Assessment During Labour
Cochrane DB Syst Rev 2013;5:CD006066 Purpose: To examine the effectiveness of continuous electronic fetal monitoring or cardiotocography during labour.
Selection Criteria: Randomized and quasi- randomized controlled trials comparing continuous CTG (with and without fetal blood sampling) to a) no fetal monitoring, b) intermittent auscultation, or c) intermittent CTG.
Results: 13 trials, 37,000 women. Continuous CTG compared with intermittent auscultation showed no difference in overall perinatal death rate or cerebral palsy rates. Nonetheless, neonatal seizures were halved (RR 0.50, 95% CI 0.31-0.80) and there was a significant increase in Cesarean sections (RR 1.63, 95% CI 1.29-2.07) and instrumental vaginal birth (RR 1.15, 95% CI 1.01-1.33) with CTG.
Conclusion: Continuous CTG may reduce the incidence of neonatal seizures, but has no effect
on cerebral palsy rates, infant mortality, or other measures of neonatal well-being. Continuous CTG was also associated with an increase in Cesarean sections and instrumental deliveries.
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describedintermsofbaselineFHR,variability(short-term,long-term),andperiodicity(accelerations, decelerations)
BaselineFHR
■ normal range is 110-160 bpm
■ parameter of fetal well-being vs. distress
Variability
■ physiologic variability is a normal characteristic of FHR
■ variability is measured over a 15 min period and is described as: absent, minimal (<6 bpm),
moderate (6-25 bpm), marked (>25 bpm)
■ normal variability indicates fetal acid-base status is acceptable
■ can only be assessed by electronic fetal monitoring (CTG)
■ variability decreases intermittently even in healthy fetus ■ see Table 19, OB35
Periodicity
■ accelerations: increase of ≥15 bpm for ≥15 s, in response to fetal movement or uterine contraction (or ≥10 bpm for ≥10 s if <32 wk GA)
■ decelerations: 3 types, described in terms of shape, onset, depth, duration recovery, occurrence, and impact on baseline FHR and variability
Table 17. Factors Affecting Fetal Heart Rate
Maternal Factors Fetal Factors
Drugs Uteroplacental
Fetal Tachycardia (FHR >160 bpm)
Fever, hyperthyroidism, anemia, dehydration
Arrhythmia, anemia, infection, prolonged activity, chronic hypoxemia, congenital anomalies
Sympathomimetics
Early hypoxia (abruption, HTN)
Chorioamnionitis
Fetal Bradycardia (FHR <110 bpm)
Hypothermia, hypotension, hypoglycemia, position, umbilical cord occlusion
Rapid descent, dysrhythmia, heart block, hyopoxia, vagal stimulation (head compression), hypothermia, acidosis
β-blockers Anesthetics
Late hypoxia (abruption, HTN) Acute cord prolapse Hypercontractility
Decreased Variability
Infection Dehydration
CNS anomalies
Dysrhythmia
Inactivity/sleep cycle, preterm fetus
Narcotics, sedatives Magnesium sulphate, β-blockers
Hypoxia