Master the board step 3

Master the Boards: USMLE Step 3
An adequate uterine
contraction
• occurs every 2–3 minutes;
• lasts 45–60 seconds; and
• has 50 mm Hg intensity.
Normal and Abnormal Labor
Stages of Labor
Labor
Stage Definition Duration Abnormalities
Stage 1—
Latent
phase
effacement
Stage 1—
Active
phase
dilation
Stage 2—
Descent
Stage 3—
Expulsion
Begins: Onset of
regular UC
Ends:
Acceleration
of cervical
dilation
Prepares cervix
for dilation
Begins:
Acceleration
of cervical
dilation
Ends: 10 cm
(complete)
Rapid cervical
dilation
Begins: 10 cm
(complete)
Ends: delivery of
baby
Descent of the
fetus
Begins: delivery
of baby
Ends: delivery of
placenta
Delivery of
placenta
< 20 hours
(primipara)
< 14 hours
(multipara)
> 1.2 cm/hour
(primipara)
> 1.5 cm/hour
(multipara)
< 2 hours
(primipara)
< 1 hour
(multipara)
+ 1 hour if
epidural
Prolonged latent phase:
1) Cervix dilated < 3 cm
2) No cervical change in 20 h (primipara)/14 h (multipara)
Cause: Most common cause is analgesia.
Management: Rest and sedation
Active phase prolongation or arrest:
1) Cervix dilated ≥ 3cm
2) Prolongation: Cervical dilation of < 1.2 cm/h (primipara) / <
1.5 cm/h (multipara)
3) Arrest: No cervical change in ≥ 2h
Cause: Abnormalities with passenger (fetal size or abnormal
presentation), pelvis, or power (dysfunctional contractions)
Management:
• Hypotonic contractions → IV oxytocin
• Hypertonic contractions → morphine sedation
• Adequate contractions → emergency cesarean section
Second-stage arrest
• Failure to deliver within 2 hours (primipara) or 1 hour
(multipara)
• Add additional 1 hour if epidural
Cause: Abnormalities with passenger, pelvis, or power
Management:
• Fetal head is not engaged → emergency cesarean
• Fetal head is engaged → trial of obstetric forceps or vacuum
extraction
< 30 minutes Prolonged third stage
• Failure to deliver placenta within 30 minutes
Cause: Consider placenta accreta/increta/percreta
Management:
• IV oxytocin
• If oxytocin fails, attempt manual removal
• Hysterectomy may be needed
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