Normal Labor & the Stages of Delivery
A Step 2 CK lesson on normal labor and the stages of delivery: the three stages with their board-tested time limits, the current ACOG 6 cm active-phase threshold and arrest criteria, distinguishing protraction from arrest, the cardinal movements, fetal deceleration interpretation (VEAL CHOP), and the "next best step" for stalled labor and non-reassuring tracings.
What Counts as Labor
Labor is regular uterine contractions that produce progressive cervical effacement and dilation. Contrast it with false labor / Braxton Hicks: irregular, non-intensifying contractions, no cervical change, relieved by hydration and rest. True labor brings regular, intensifying contractions, bloody show, and documented cervical change.
Labor is divided into three stages (some texts add a 4th = the first ~2 h postpartum). On Step 2 CK the task is almost always the same three-part reasoning:
- Identify which stage/phase the patient is in.
- Judge progress — normal, protracted (too slow), or arrested (stopped).
- Pick the next best step — expectant management, oxytocin augmentation, or cesarean delivery.
- Stage 1 = onset of regular contractions → full dilation (10 cm). Split into latent (0 → 6 cm) and active (6 → 10 cm). Contemporary ACOG active-phase threshold is 6 cm, not the old 4 cm.
- Active-phase arrest = ≥6 cm + ruptured membranes with no cervical change for ≥4 h of adequate contractions or ≥6 h if contractions are inadequate.
- Stage 2 = full dilation → delivery of infant. Prolonged if nullipara >3 h (>4 h with epidural) or multipara >2 h (>3 h with epidural).
- Stage 3 = delivery of infant → delivery of placenta. Retained placenta if >30 min.
- Adequate contractions = ≥200 Montevideo units (MVU) in 10 min (summed peak amplitudes above baseline, measured by intrauterine pressure catheter).
- Station = presenting part relative to the ischial spines, scaled −5 to +5; 0 = engaged (presenting part at the spines).
Stages of Labor at a Glance
| Stage | Starts → Ends | Normal upper limit | Key point |
|---|---|---|---|
| 1 – Latent | Regular contractions → 6 cm | Nullip <20 h, Multip <14 h | Slow dilation is normal; do NOT diagnose arrest here |
| 1 – Active | 6 cm → 10 cm (full) | ~4–6 h | Fastest dilation; where arrest of dilation is diagnosed |
| 2 | Full dilation → delivery of infant | Nullip ≤3 h (≤4 h epidural); Multip ≤2 h (≤3 h epidural) | Cardinal movements; arrest of descent |
| 3 | Delivery of infant → delivery of placenta | ≤30 min | Watch for PPH; active management |
Buzzwords: G1P0 at 40 wk in active labor; cervix 6 cm for 4 hours; membranes ruptured; contractions 220 MVU; no cervical change.
Diagnosis: Arrest of the active phase (labor dystocia) — the single most common indication for a primary cesarean.
NEXT BEST STEP → Cesarean delivery. Contractions are already adequate (≥200 MVU) and ≥4 h have passed at ≥6 cm with ruptured membranes and no change, so more oxytocin adds no benefit.
Flip the switch: if contractions were inadequate (<200 MVU), the next step would instead be oxytocin augmentation ± amniotomy, then reassess — not cesarean.
- Protraction = labor slower than expected but still progressing → augment (oxytocin ± amniotomy), especially if contractions are inadequate.
- Arrest = no progress despite adequate forces (≥6 cm, ROM, adequate contractions) → cesarean.
- Always work through the 3 Ps: Power (contraction strength / MVU), Passenger (fetal size, position, malpresentation), Passage (maternal pelvis).
- A prolonged latent phase alone is NOT an indication for cesarean — give time, rest, hydration, or augmentation.
- Only diagnose active-phase arrest at ≥6 cm with ruptured membranes — never in the latent phase.
VEAL CHOP — map each fetal heart-rate deceleration to its cause:
- Variable → Cord compression
- Early → Head compression
- Accelerations → Okay (reassuring)
- Late → Placental (uteroplacental) insufficiency
Cardinal movements of labor, in order: Engagement → Descent → Flexion → Internal rotation → Extension → External rotation (restitution) → Expulsion.
Note: external rotation and restitution are the same movement — count them as one step, so there are seven cardinal movements, not eight.
Decelerations & the Next Step
| Deceleration | Shape / timing | Cause | Next best step |
|---|---|---|---|
| Early | Mirrors contraction; nadir = peak | Fetal head compression (vagal) | None — benign; continue monitoring |
| Variable | Abrupt V/W drop, variable timing | Umbilical cord compression | Reposition mother; amnioinfusion if recurrent |
| Late | Gradual; nadir AFTER the peak | Uteroplacental insufficiency | Intrauterine resuscitation; deliver if persistent |
Buzzwords: oxytocin infusing; recurrent decelerations whose nadir falls after the contraction peak; minimal/absent variability.
Diagnosis: Recurrent late decelerations = uteroplacental insufficiency (Category II, trending toward III with absent variability).
NEXT BEST STEP → Intrauterine resuscitation:
- Reposition to left lateral decubitus
- Stop the oxytocin
- IV fluid bolus; supplemental O2 may be given (routine benefit is unproven, but it remains a standard bundle element)
- Consider a tocolytic (e.g., terbutaline) if tachysystole
If the tracing does not recover (Category III / sinusoidal) → expedite delivery (operative vaginal or cesarean).
- GBS screening at 36 0/7 – 37 6/7 wk. Give intrapartum penicillin G if: culture-positive, unknown status with risk factors (preterm, ROM ≥18 h, intrapartum fever), prior GBS-affected infant, or GBS bacteriuria this pregnancy. Penicillin-allergic → cefazolin (low-risk allergy); if high-risk/anaphylaxis, clindamycin only if the isolate is susceptible, otherwise vancomycin.
- Bishop score ≥8 = favorable cervix (induction likely to succeed); ≤6 = unfavorable → cervical ripening (prostaglandins or a Foley/mechanical balloon).
- Active management of the third stage — oxytocin after delivery, controlled cord traction, uterine massage — reduces postpartum hemorrhage (the #1 third-stage board move).
- Delayed cord clamping ≥30–60 s for vigorous term and preterm neonates.
- Confirm rupture of membranes with pooling, nitrazine (turns blue), and ferning.
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