Intrapartum Fetal Monitoring
On this page
Direct answer
A normal fetal heart rate lies between 110 and 160 beats per minute, and intrapartum monitoring is the discipline of reading deviations against contractions: tachycardia above 160 suggests fever, hypoxia, drugs or chorioamnionitis; bradycardia below 110 is an ominous late finding when sustained; and decelerations are classified by timing — early (mirror the contraction, head compression, benign), late (begin after the contraction peak, uteroplacental insufficiency, the signature of placental failure) and variable (abrupt onset, variable shape, cord compression, the commonest and usually positional). Low-risk labours are monitored by intermittent auscultation — listening for a full minute every 30 minutes in the first stage and every 15 minutes in the second — while high-risk labours (growth restriction, meconium, oxytocin, previous caesarean, fever) get continuous cardiotocography. When a trace is suspicious, resuscitate in utero (left lateral, fluids, stop oxytocin, oxygen by mask) and, if it fails to recover, deliver; fetal scalp blood pH below 7.20 confirms acidosis and mandates delivery.
What you must remember
- Baseline and bands: normal 110-160 bpm; tachycardia over 160 (fever, chorioamnionitis, hypoxia, beta-agonists); bradycardia below 110 — sustained bradycardia below 100 means severe hypoxia until proven otherwise; baseline variability of 6-25 bpm is the single best sign of fetal wellbeing.
- Early decelerations: shallow, slow, mirror-image with onset before the contraction peak and return to baseline by its end — vagal response to head compression; not pathological in the second stage.
- Late decelerations: onset after the contraction peak, nadir delayed, recovery after the contraction ends — uteroplacental insufficiency; repetitive late decelerations with reduced variability are the classic pre-arrest pattern.
- Variable decelerations: abrupt fall of 15 bpm or more within seconds, variable duration and shape, often with shoulders — umbilical cord compression; changing the maternal position and amnioinfusion for recurrent variables with oligohydramnios relieve them.
- Auscultation intervals (intermittent): every 30 minutes in the first stage, every 15 minutes in the second stage, for one full minute including after a contraction.
- Continuous CTG indications: meconium-stained liquor, abnormal FHR on auscultation, oxytocin augmentation, growth restriction, preterm labour, fever, bleeding, previous caesarean in labour, multiple pregnancy.
- Intrauterine resuscitation: left lateral position, intravenous fluids, stop oxytocin, oxygen by face mask, treat hypotension, tocolysis for hyperstimulation — the "next step" answer for an abnormal trace before deciding delivery.
- Fetal scalp blood sampling: pH 7.25 or above normal, 7.21-7.24 borderline (repeat in 30 minutes), 7.20 or below acidosis — expedited delivery; scalp stimulation causing an acceleration is a bedside alternative suggesting pH above 7.20.
Decelerations walked through on a trace
Draw the trace in your head. Contractions peak every three minutes; the heart dips starting after each peak, its lowest point trailing the contraction's lowest point by 20-plus seconds, recovering only after the contraction has finished — late decelerations, repeated with every contraction and with flattening variability. This is the placenta failing: hypertension, growth restriction or an abruption-haematoma background fits. The first responses are intrauterine resuscitation — left lateral, fluids, oxytocin off, oxygen — and reassess. Variability returning with decelerations resolving means labour may cautiously proceed; decelerations deepening into prolonged bradycardia mean theatre.
Now a different trace: abrupt drops from a 140 baseline to 70 within seconds, V- or W-shaped, at unpredictable times relative to contractions, recovering equally fast — variables. The cord is being squeezed, most often by nuchal encirclement or oligohydramnios; position change first (knee-chest or opposite lateral), and if variables recur with oligohydramnios at term, amnioinfusion cushions the cord. The third pattern is a gentle, symmetrical dip that begins, bottoms and recovers in phase with the contraction itself — an early deceleration of head compression in the second stage, observed, not acted upon. Three shapes, three mechanisms, three different management lanes — that is the whole of cardiotocography for the screening exam, with the prolonged deceleration over 3 minutes as the emergency wildcard that goes straight to resuscitate-and-deliver.
Recall magnets
The marks sit in pairings: late with placenta, variable with cord, early with head. The second magnet is the auscultation interval (30/15 minutes) — asked verbatim. The third is variability as the best single marker of wellbeing, and the fourth the scalp pH cut-off 7.20 — with the tempting distractor "7.30" for the delivery threshold. Meconium with an abnormal trace outranks meconium alone; the answer to "thick meconium plus late decelerations" is expedited delivery, not observation.
Frequently asked questions
What is the normal fetal heart rate baseline in labour?
110 to 160 beats per minute, with baseline variability of 6-25 bpm; variability is the most reliable single index of fetal oxygenation.
How do late decelerations differ from early decelerations?
Late decelerations begin after the contraction peak and recover after it ends, reflecting uteroplacental insufficiency; early decelerations mirror the contraction, reflecting physiologic head compression.
What causes variable decelerations and how are they relieved?
Umbilical cord compression — abrupt V-shaped drops; maternal repositioning relieves most, and amnioinfusion helps recurrent variables with oligohydramnios.
What are the auscultation intervals for intermittent monitoring in low-risk labour?
Listen for one full minute every 30 minutes in the first stage and every 15 minutes in the second stage, immediately after a contraction.
At what fetal scalp blood pH is delivery indicated?
At pH 7.20 or below; values of 7.21-7.24 are repeated within 30 minutes, and 7.25 or more are reassuring.