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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- First stage: onset of labor to complete dilation; active labor generally begins at 6 cm
- Second stage: complete dilation to delivery; third stage: delivery to placenta
- Labor dystocia should not be diagnosed too early
- Category III fetal heart tracing requires resuscitation and expedited delivery if not corrected
- Major cesarean indications include placenta previa, prior classical incision, uterine rupture, persistent Category III tracing, and some malpresentations
Overview
Labor is progressive cervical effacement/dilation and fetal descent resulting in delivery. Active labor begins around 6 cm. Management balances safe patience with timely intervention.
Epidemiology
Cesarean delivery accounts for a substantial minority of US births. Avoiding unnecessary primary cesarean reduces future previa/accreta and surgical risks, but cesarean is lifesaving when maternal or fetal safety is threatened.
Clinical Features
Symptoms
Regular painful contractions increasing in frequency/intensity
Rupture of membranes or bloody show
Urge to push and rectal pressure in second stage
Severe abdominal pain with loss of station suggests uterine rupture
Heavy bleeding suggests previa, abruption, rupture, or laceration
Signs
Cervical dilation/effacement with fetal descent
Active labor begins at about 6 cm
Adequate contractions can be measured clinically or with IUPC
Category III tracing: absent variability with recurrent late/variable decels, bradycardia, or sinusoidal pattern
Turtle sign suggests shoulder dystocia
Investigations
First-line
Cervical examinationDilation, effacement, station, position, presentation; avoid with unexplained bleeding until previa excluded
Fetal heart monitoringCategory I reassuring; II indeterminate; III abnormal
Contraction assessmentFrequency/duration/strength; MVU >=200 if IUPC used
Second-line
Bedside ultrasoundConfirm presentation, placental location, fetal number, position
Maternal labsCBC, type/screen, infectious labs, preeclampsia labs if indicated
ROM assessmentMembrane status affects labor management/infection risk
Specialist
Operative vaginal delivery assessmentComplete dilation, ruptured membranes, engaged head, known position, adequate pelvis, anesthesia, and cesarean capability
Cesarean decisionBased on fetal status, labor progress, presentation, placenta, uterine scar, and maternal condition
1
Stages
- First stage latent: onset to active phase
- First stage active: about 6 cm to 10 cm
- Second stage: 10 cm to infant delivery
- Third stage: infant delivery to placenta
- Fourth stage: immediate postpartum recovery/hemorrhage surveillance
2
Labor dystocia
- Do not diagnose active-phase arrest before 6 cm
- Active-phase arrest requires no cervical change despite adequate time/contractions
- Manage with amniotomy, oxytocin, positioning, and assessment of power/passenger/pelvis
- Cesarean if arrest criteria met and safe vaginal delivery not progressing
3
Fetal heart tracing
- Category I: routine care
- Category II: reposition, IV fluids, stop oxytocin, treat tachysystole, consider amnioinfusion for variables
- Category III: resuscitation and expedited delivery if unresolved
- Late decels = uteroplacental insufficiency; variable decels = cord compression
4
Emergencies
- Cesarean for previa, vasa previa, rupture, persistent Category III, failed operative delivery, arrest, unsuitable malpresentation, active genital HSV, prior classical incision
- Shoulder dystocia: call help, McRoberts, suprapubic pressure, posterior arm, rotational maneuvers; avoid fundal pressure
- Cord prolapse: elevate presenting part and urgent cesarean unless vaginal delivery imminent
Complications
- Postpartum hemorrhage: Atony, trauma, retained tissue, coagulopathy
- Shoulder dystocia: Brachial plexus injury, clavicle fracture, hypoxia
- Uterine rupture: Fetal bradycardia, pain, loss of station, shock
- Chorioamnionitis: Fever, uterine tenderness, fetal tachycardia, prolonged ROM
- Cesarean complications: Infection, hemorrhage, thromboembolism, adhesions, future accreta risk
USMLE Step 2 CK Exam Tips
- 1Active labor starts at 6 cm
- 2First stage = dilation to 10 cm; second = baby; third = placenta
- 3Late decelerations = uteroplacental insufficiency; variable = cord compression
- 4Category III tracing not corrected = expedited delivery
- 5Shoulder dystocia first maneuver = McRoberts plus suprapubic pressure
- 6Never use fundal pressure in shoulder dystocia
- 7Placenta previa = cesarean
- 8Prior classical incision = repeat cesarean before labor
practicetest your knowledge on labor & delivery (stages, dystocia, indications for c-section)Apply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — obstetrics & gynecology and beyond.
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