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Cervical change is the whole test for true labor. Active labor starts at 6 cm, not 4. Late decelerations mean uteroplacental insufficiency. This episode walks through normal labor and how to assess the laboring patient the way it actually gets tested: the four stages, the cardinal movements, station, confirming rupture of membranes, and the fetal heart rate tracing, including the one number that separates a uterus that is doing its job from one that is not.
Normal Labor: Stages and Mechanisms
Regular uterine contractions producing progressive cervical effacement and dilation, ending in delivery of the fetus and placenta. Two numbers drive every decision in labor: dilation (how open) and station (how low).
True Labor vs False Labor
- True labor: regular contractions getting closer together and stronger, with cervical change on repeated exams.
- Pain starts in the back and wraps to the abdomen.
- Rest and hydration don’t stop it.
- False labor (Braxton Hicks): irregular, no cervical change, lower abdominal pain only, relieved by rest, hydration, or walking.
- Cervical change is the whole test. Contractions without it are not labor.
- Bloody show: passage of the blood-streaked mucus plug. Labor is near, but it isn’t a stage.
- The question stem would likely describe a woman with contractions and ask whether to admit her. It turns on repeated cervical exams, not on how the contractions feel.
The Four Stages
- First stage: onset of labor → complete dilation (10 cm). The longest stage.
- Latent phase: 0 to 6 cm. Slow and highly variable. A prolonged latent phase by itself is not an indication for cesarean.
- Active phase: 6 to 10 cm. Dilation accelerates. Progress gets judged against the arrest criteria rather than a fixed hourly rate.
- Arrest of active labor: ≥6 cm, ruptured membranes, and no cervical change for ≥4 hours with adequate contractions or ≥6 hours with inadequate contractions.
- Second stage: complete dilation → delivery of the infant.
- Nulliparous up to 3 hours, multiparous up to 2 hours.
- With an epidural, add an hour to each: 4 hours nullip, 3 hours multip.
- Third stage: delivery of the infant → delivery of the placenta. Delivered within 30 minutes with active management. Past 30 minutes = retained placenta.
- Fourth stage: the first 1 to 2 hours postpartum. Uterine tone and hemorrhage watch.
Cardinal Movements
- How the fetal head negotiates the pelvis: engagement → descent → flexion → internal rotation → extension → external rotation (restitution) → expulsion.
- Engagement = the biparietal diameter passes the pelvic inlet, putting the head at station 0.
- Internal rotation brings the occiput anterior. Failure to rotate leaves persistent occiput posterior: longer pushing, more back pain.
Exam Keys
- Labor = contractions plus cervical change. No change = false labor.
- Active phase starts at 6 cm, not 4. A slow latent phase is normal.
- Second stage: nullip 3 hours, multip 2 hours, plus an hour with an epidural.
- Placenta not delivered by 30 minutes with active management = retained placenta.
- Station 0 = head at the ischial spines = engaged.
Assessing the Laboring Patient
The bedside evaluation that establishes where the fetus is, how the cervix is progressing, and whether the fetus is tolerating labor. Three things get rechecked over and over: the cervix, the fetal position, and the tracing.
Fetal Orientation
- Lie: fetal spine relative to maternal spine. Longitudinal (normal), transverse, or oblique.
- Presentation: the part entering the pelvis first. Cephalic (normal), breech, or shoulder.
- Position: where the occiput points in the maternal pelvis. Occiput anterior is favorable. Full head flexion presents the smallest diameter.
- Leopold maneuvers: four abdominal palpations establishing lie, presentation, and position at the bedside.
Cervical Exam and Station
- Dilation 0 to 10 cm.
- Effacement 0 to 100% thinning.
- Station: the presenting part relative to the ischial spines, graded -5 to +5 cm. Station 0 = at the spines = engaged. Positive numbers are below the spines.
Membrane Status
- Confirm rupture of membranes with the triad:
- Pooling of fluid in the posterior fornix (the recess behind the cervix at the top of the vagina) on speculum exam.
- Nitrazine paper turning blue. Amniotic fluid pH 7.1 to 7.3 against a normal vaginal pH of 3.8 to 4.5.
- Ferning: dried amniotic fluid crystallizes into a fern-leaf pattern on the slide.
- Blood, semen, and bacterial vaginosis all cause false-positive nitrazine.
Fetal Heart Rate Monitoring
- Baseline: 110 to 160 bpm. Under 110 = bradycardia. Over 160 = tachycardia, which should make you think maternal fever or chorioamnionitis.
- Variability: fluctuation around the baseline and the best indicator of fetal oxygenation. Moderate (6 to 25 bpm) is reassuring. Minimal (≤5 bpm) or absent is not.
- Accelerations: ≥15 bpm above baseline for ≥15 seconds. Reassuring.
- Early decelerations: mirror the contraction, nadir with the peak → head compression. Benign.
- Variable decelerations: abrupt drop, no fixed timing with the contraction → cord compression. The most common in labor.
- Late decelerations: begin after the peak, recover after the contraction ends → uteroplacental insufficiency. The concerning one.
- The question stem would likely describe a tracing in words rather than show it. Match shape and timing to mechanism.
Tracing Categories
- Category I: baseline 110 to 160, moderate variability, no late or variable decelerations. Early decelerations may be present → normal. No intervention, continue routine monitoring.
- Category II: anything that is not I or III → indeterminate. Evaluate and keep watching.
- Category III: absent variability with recurrent late or variable decelerations or bradycardia, or a sinusoidal pattern → abnormal. Act now.
Contraction Adequacy
- The external belt shows how often she contracts, not how hard. When labor stalls, hard is the question.
- Intrauterine pressure catheter (IUPC): catheter placed inside the uterus, measuring contraction strength directly. Requires ruptured membranes.
- Montevideo units (MVUs): add the peak-above-baseline pressure of every contraction in 10 minutes. Five contractions peaking 50 mmHg above baseline = 250 MVUs.
- ≥200 MVUs = adequate labor. This is the number that separates the two stalls:
- Stalled 4 hours at ≥200 → the uterus is doing its job → true arrest → cesarean.
- Stalled under 200 → contractions too weak → oxytocin, and it is not arrest until 6 hours without change on oxytocin.
Exam Keys
- Station 0 = ischial spines = engaged.
- Ruptured membranes = pooling + nitrazine blue + ferning.
- Moderate variability is the best single sign of fetal well-being.
- Early decels = head compression. Variable decels = cord compression. Late decels = uteroplacental insufficiency.
- Absent variability with recurrent late decelerations = Category III = act now.
- ≥200 MVUs = adequate contractions.
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