Reproductive · Obstetrics
The facts most likely to be tested
The first stage of labor is defined as the time from the onset of regular uterine contractions to complete cervical dilation (10 cm).
Active labor is defined by the ACOG as cervical dilation of ≥6 cm with regular, painful contractions.
Protraction disorder occurs when the rate of cervical change is slower than the 1st percentile of the labor curve, while arrest of labor is defined as no cervical change for ≥4 hours with adequate contractions or ≥6 hours with inadequate contractions.
Cardinal movements of labor follow the sequence of engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion.
Category I fetal heart rate tracings are normal, characterized by a baseline of 110–160 bpm, moderate variability, and the absence of late or variable decelerations.
Late decelerations are caused by uteroplacental insufficiency and require immediate intervention, starting with maternal repositioning to the lateral decubitus position.
Variable decelerations are associated with umbilical cord compression and are typically resolved by changing maternal position to relieve cord pressure.
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A 28-year-old G1P0 woman at 39 weeks gestation presents to the labor and delivery unit with regular, painful contractions. On examination, her cervix is 6 cm dilated and 90% effaced. The fetal heart rate tracing shows a baseline of 140 bpm with moderate variability and no decelerations. Two hours later, the cervix remains 6 cm dilated despite adequate uterine activity as measured by an intrauterine pressure catheter. The patient is afebrile and the fetus is in a vertex presentation.
What is the most appropriate classification for this patient's labor progress?
Protraction disorder
The patient is in the active phase of labor (≥6 cm) and is experiencing a rate of cervical change slower than the expected threshold, which defines a protraction disorder.
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Etiology / Epidemiology
Labor is the rhythmic, progressive uterine contractions leading to cervical change. Nulliparity is the primary risk factor for prolonged labor.
Clinical Manifestations
Defined by regular contractions and cervical dilation. 10 cm is the threshold for full dilation.
Diagnosis
Clinical diagnosis based on cervical change and regular contractions. Partogram is the gold standard for monitoring progress.
Treatment
Supportive care, oxytocin for augmentation, and amniotomy. Avoid elective induction before 39 weeks.
Prognosis
Most progress to spontaneous vaginal delivery. Postpartum hemorrhage is the primary maternal risk.
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Epidemiology & Etiology
Labor typically occurs between 37 and 42 weeks gestation. It is initiated by a complex interplay of fetal cortisol, estrogen, and prostaglandins. Nulliparity significantly increases the duration of the first stage of labor.
Pertinent Anatomy
The pelvic inlet and pelvic outlet determine the mechanical feasibility of delivery. The fetal head must undergo cardinal movements (engagement, descent, flexion, internal rotation, extension, external rotation, expulsion) to navigate the maternal pelvis.
Pathophysiology
The process begins with cervical ripening mediated by prostaglandins and collagen degradation. Uterine contractions are driven by oxytocin release and increased gap junction formation in the myometrium. The Ferguson reflex (fetal head pressure on the cervix) triggers further oxytocin release, creating a positive feedback loop.
Clinical Manifestations
Labor is divided into three stages: Stage 1 (latent/active), Stage 2 (pushing), and Stage 3 (placental delivery). Active labor is defined by regular contractions and cervical dilation of ≥6 cm. Fetal bradycardia or variable decelerations on the fetal heart rate monitor are red flags for umbilical cord compression or fetal distress.
Diagnosis
Diagnosis is clinical: regular, painful contractions associated with progressive cervical effacement and dilation. The Partogram is the gold standard tool to plot cervical dilation over time to identify protracted labor. A dilation rate of <1.2 cm/hr in nulliparous women suggests arrest of labor.
Treatment
Management includes continuous fetal monitoring and maternal hydration. Oxytocin is the first-line agent for labor augmentation. Amniotomy (artificial rupture of membranes) may be used to accelerate progress. Do not use prostaglandins in patients with a prior classical cesarean section due to risk of uterine rupture.
Prognosis
Most patients achieve vaginal delivery within 24 hours. Postpartum hemorrhage (defined as >500mL blood loss) is the most common complication. Close monitoring for uterine atony is required in the immediate postpartum period.
Differential Diagnosis
False labor: irregular contractions without cervical change
Preterm labor: labor occurring before 37 weeks gestation
Chorioamnionitis: maternal fever and fetal tachycardia
Placental abruption: painful vaginal bleeding with hypertonic uterus
Uterine rupture: loss of fetal station and severe abdominal pain