Intrapartum Fetal Surveillance UNC School of Medicine Obstetrics and Gynecology Clerkship Case Based Seminar Series

Objectives Review techniques of fetal monitoring Review how to interpret electronic fetal monitoring

ACOG Recommendation High risk pregnancies should be monitored continuously during labor » Examples: preeclampsia, growth restriction, T1DM Intermittent auscultation is acceptable in uncomplicated patients

Intrapartum Fetal Surveillance What is it? » Measurement of fetal status Can include: fetal heart rate, blood gases, amniotic fluid volume, fetal stimulation responses Why do we do it? » Allows for recognition of changes in fetal oxygenation that can lead to permanent neurologic disability

Electronic Fetal Monitoring Can be performed internally or externally » External monitor uses a Doppler device » Internal monitor – a wire/electrode is placed on fetal scalp External monitoring as reliable as internal Used when externally derived tracing has poor technical quality (positional) Can be intermittent or continuous Fetal heart rates are described by: » Rate » Baseline » Variability » Presence of accelerations » Presence of decelerations » Changes in trend over time Uterine contractions also measured

Fetal Heart Rate Baseline = mean FHR during a 10 minute segment » Baseline must be for a minimum of 2 min in any 10 min segment Bradycardia = <110 beats per min Tachycardia = >160 beats per min » What are some causes of fetal tachycardia? Chorioamnionitis, medication, thyrotoxicosis, etc.

Variability Determined in a 10 minute window Visually quantitated by amplitude of peak-to-trough » Absent = undetectable » Minimal = <5 bpm » Moderate = 6 to 25 bpm Reassuring » Marked = >25 bpm

Accelerations What is an acceleration? » An increase in FHR above baseline » Duration of acceleration = time from initial change to return to baseline » Onset to peak = < 30 seconds Before 32 weeks gestation » Acceleration reaches highest point (acme) at 10 beats per min or more above baseline » Duration greater than 10 sec, but less than 2 min At 32 weeks and greater » Acceleration has an acme at 15 beats per min or more above baseline » Duration greater than 15 sec, but less than 2 min Prolonged deceleration = 2 minutes or more Change in baseline = 10 min or more

Decelerations They are a decrease in FHR from baseline Types of decelerations » Early Gradual onset, onset to nadir 30 sec or more Associated with uterine contraction » Nadir of deceleration = peak of contraction » Late Gradual onset, onset to nadir 30 sec or more Associated with uterine contraction » Onset, nadir and recovery occur after the onset, peak and end of contraction respectively » Variable Abrupt onset, onset to nadir is less than 20 sec Decrease in FHR 15 bpm of more Duration 15 sec or more, but less than 2 min » Prolonged deceleration = greater than 2 min, but less than 10

Decelerations What causes them? » Early – these are considered physiologic Pressure of fetal head in birth canal Digital examination Forceps application » Late Uteroplacental insufficiency » Variable Umbillical cord compression Oligohydramnios

Decelerations – Treatment Interventions Pelvic exam (rule out prolapsed cord) Maternal oxygen Change maternal position Correct maternal hypotension Discontinue oxytocin Amnioinfusion Scalp stimulation Tocolytics for uterine hyperstimulation

FHR Interpretation System What are the characteristics of a reassuring FHR pattern? » A baseline FHR of 110 to 160 bpm » Moderate variability » Early accelerations may or may not be present » No late decelerations » No variable decelerations » Age appropriate accelerations

Category III FHR Tracing Increased risk for hypoxemia and fetal acidemia If conservative measures do not work, you can » Perform ancillary test to further characterize fetal status Scalp blood sampling for pH and lactate Pulse oximetry » Deliver

Uterine Contractions Quantitated using Montevideo units when using pressure transducers Montevideo units are calculated by – peak strength (mm Hg) X # of contractions in 10 minutes Adequate contractions = 200 to 250 Montevideo units Or a rough measure, adequate contractions = 3 to 5 contractions in 10 minutes

Bottom Line Concepts Intrapartum fetal surveillance is a way of measuring fetal status The baseline fetal heart rate is between 110 and 160 Signs of a reassuring FHR pattern include moderate variability and occasional accelerations. There should be concern for fetal acidemia with the combination of absent or minimal baseline variability and late of variable decelerations Transient changes in FHR pattern are expected/considered physiologic when in response to descent or uterine contraction for example Corrective interventions for non-reassuring FHR include: discontinuing uterotonic drugs, changing maternal positions, correcting hypotension with IV fluids and administering supplemental oxygen +/- delivery